Method for output layer set mode in multilayered video stream

ABSTRACT

A method of decoding may comprise: receiving a bitstream comprising compressed video/image data; parsing or deriving, from the bitstream, an output layer set mode indicator in a video parameter set (VPS); identifying output layer set signaling based on the output layer set mode indicator; identifying one or more picture output layers based on the identified output layer set signaling; and decoding the identified one or more picture output layers.

PRIORITY INFORMATION

This application is a Continuation of U.S. application Ser. No.17/544,164, filed on Aug. 21, 2020, which is a Continuation of U.S.application Ser. No. 17/000,018, filed on Aug. 21, 2020, now U.S. Pat.No. 11,228,776, patented on Jan. 18, 2022; which is a Non-ProvisionalApplication that claims priority from U.S. Provisional Application No.63/001,045, filed on Mar. 27, 2020, the entire contents of which areincorporated herein by reference in their entireties.

BACKGROUND Field

This disclosure is related to video compression technologies andinter-prediction and intra-prediction in advanced video codec. Inparticular, the disclosure is related to next-generation video codingtechnologies including video coding/decoding technologies beyond HighEfficiency Video Coding (HEVC), such as Versatile Video Coding (VVC).More specifically, an aspect of the disclosure is directed to a method,an apparatus and computer-readable medium that provide a set of advancedvideo coding technologies designed output layer derivation in a codedvideo stream with multiple layers.

Description of Related Art

Video coding and decoding using inter-picture or intra-pictureprediction with motion compensation has been known for decades.Uncompressed digital video can consist of a series of pictures, eachpicture having a spatial dimension of, for example, 1920×1080 luminancesamples and associated chrominance samples. The series of pictures canhave a fixed or variable picture rate (informally also known as framerate), of, for example 60 pictures per second or 60 Hz. Uncompressedvideo has significant bitrate requirements. For example, 1080p60 4:2:0video at 8 bit per sample (1920×1080 luminance sample resolution at 60Hz frame rate) requires close to 1.5 Gbit/s bandwidth. An hour of suchvideo may require more than 600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce aforementioned bandwidth or storage space requirements,in some cases by two orders of magnitude or more. Both lossless andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and a video decoder can utilize techniques from severalbroad categories, including, for example, motion compensation,transform, quantization, and entropy coding, some of which will beintroduced below.

Historically, video encoders and decoders tended to operate on a givenpicture size that was, in most cases, defined and stayed constant for acoded video sequence (CVS), Group of Pictures (GOP), or a similarmulti-picture timeframe. For example, in Motion Picture Experts Group(MPEG)-2, system designs are known to change the horizontal resolution(and, thereby, the picture size) dependent on factors such as activityof the scene, but only at Intra-frame (or i-frame, or i-picture), hencetypically for a GOP. The resampling of reference pictures for use ofdifferent resolutions within a CVS is known, for example, from ITU-TRec. H.263 Annex P. However, here the picture size does not change, onlythe reference pictures are being resampled, resulting potentially inonly parts of the picture canvas being used (in a case of downsampling),or only parts of the scene being captured (in a case of upsampling).Further, H.263 Annex Q allows the resampling of an individual macroblockby a factor of two (in each dimension), upward or downward. Again, thepicture size remains the same. The size of a macroblock is fixed inH.263, and therefore does not need to be signaled.

Changes of picture size in predicted pictures became more mainstream inmodern video coding. For example, VP9 allows reference pictureresampling and change of resolution for a whole picture. Similarly,certain proposals made towards Versatile Video Coding (VVC) (including,for example, Hendry, et. al, “On adaptive resolution change (ARC) forVVC”, Joint Video Team document JVET-M0135-v1, Jan. 9-19, 2019,incorporated herein in its entirety) allow for resampling of wholereference pictures to different—higher or lower—resolutions. In Hendry,different candidate resolutions are suggested to be coded in thesequence parameter set and referred to by per-picture syntax elements inthe picture parameter set.

SUMMARY

Disclosed are techniques for signaling of adaptive picture size in avideo bitstream according to various embodiments.

According to an aspect of the disclosure, a method of decoding maycomprise: receiving a bitstream comprising compressed video/image data,wherein the bitstream has multiple layers; parsing or deriving, from thebitstream, an output layer set mode indicator in a video parameter set(VPS); identifying output layer set signaling based on the output layerset mode indicator; identifying one or more picture output layers basedon the identified output layer set signaling; and decoding theidentified one or more picture output layers.

The identifying of the output layer set signaling based on the outputlayer set mode indicator may include: in a case that the output layerset mode indicator in the VPS is a first value, identifying a highestlayer in the bitstream as the one or more picture output layers; in acase that the output layer set mode indicator in the VPS is a secondvalue, identifying all layers in the bitstream as the one or morepicture output layers; and in a case that the output layer set modeindicator in the VPS is a third value, identifying the one or morepicture output layers based on explicit signaling in the VPS.

The first value may be different from the second value and may bedifferent from the third value, and the second value may be differentfrom the third value.

The first value may be 0, the second value may be 1, and the third valuemay be 2. However, other values may be used and the disclosure is notlimited to usage of 0, 1 and 2 as described above.

The identifying the one or more picture output layers by the explicitsignaling in the VPS may include: (i) parsing or deriving, from the VPS,an output layer flag, and (ii) setting layers that have the output layerflag equal to 1 be the one or more picture output layers.

The identifying of the output layer set signaling based on the outputlay set mode indicator may include: in a case that the output lay setmode indicator in the VPS is a predetermined value, the output layer setsignaling includes identifying the one or more picture output layersbased on explicit signaling in the VPS.

The identifying the one or more picture output layers by the explicitsignaling in the VPS includes: (i) parsing or deriving, from the VPS, anoutput layer flag, and (ii) setting layers that have the output layerflag equal to 1 be the one or more picture output layers, wherein anumber of the multiple layers is greater than 2.

The output layer set signaling may include identifying the one or morepicture output layers based on the explicit signaling in the VPS whenthe output layer set mode indicator equals 2, and a number of layers ofthe multiple layers is greater than 2.

The output layer set signaling may include identifying the highest layerin the bitstream or all layers in the bitstream as the one or morepicture output layers by inferring the one or more picture outputlayers, when the output layer set mode indicator is less than 2, and thenumber of multiple layers is 2, and the output layer set mode indicatoractually is less than 2, and the number of multiple layers actually is2.

According to an embodiment, a number output layer sets minus1 indicatorin the VPS indicates a number of the output layer set.

According to an embodiment, a VPS maximum layer minus1 indicator in theVPS indicates a number of layers in the bitstream.

According to an embodiment, the output layer set flag [i][j] in the VPSindicates whether a j-th layer of an i-th output layer set is an outputlayer or not.

According to an embodiment, if all of the multiple layers areindependent where a VPS all independent layers flag of the VPS equals 1,the output layer set mode indicator is not signaled, and a value of theoutput layer set mode indicator is inferred to be the second value.

According to an embodiment, when each layer is an output layer set, apicture output flag of the VPS is set equal to a picture output flagsignaled in a picture header, regardless of the value of the outputlayer set mode indicator.

Note: a picture in an output layer may or may not have aPictureOutputFlag equal to 1. A picture in a non-output layer has aPictureOutputFlag equal to 0. A picture with PictureOutputFlag equal to1 is outputted for display. A picture with PictureOutputFlag equal to 0is not outputted for display.

According to an embodiment, a picture output flag is set equal to 0 whena sequence parameter set (SPS) VPS identifier is greater than 0, whichindicates that more than one layer is present in the bitstream, an eachlayer is an output layer set flag of the VPS is equal to 0, whichindicates that the multiple layers in the bitstream are not allindependent, the output layer set mode indicator is equal to 0 and acurrent access unit contains a picture that satisfies all of thefollowing conditions including: having a picture output flag that isequal to 1, having a nuh layer identifier that is greater than that of acurrent picture and belongs to the output layer of the output layer set.

According to an embodiment, a picture output flag of the VPS is setequal to 0 when a sequence parameter set (SPS) of the VPS is greaterthan 0, an each layer is an output layer set flag is equal to 0, theoutput layer set mode indicator is equal to 2, and the output layer setoutput layer flag [Target OLS Index][General Layer Index [nuh layeridentifier] ] is equal to 0.

According to an embodiment, the method may further comprise: controllinga display to display the decoded one or more picture output layers.

According to an aspect of the disclosure, a non-transitorycomputer-readable storage medium storing instructions that, whenexecuted, cause a system or device comprising one or more processors to:receive a bitstream comprising compressed video/image data, wherein thebitstream has multiple layers; parse or derive, from the bitstream, anoutput layer set mode indicator in a video parameter set (VPS); identifyoutput layer set signaling based on the output layer set mode indicator;identify one or more picture output layers based on the identifiedoutput layer set signaling; and decode the identified one or morepicture output layers.

According to an embodiment, the instructions are further configured tocause the system or device comprising the one or more processors to:control a display to display the decoded one or more picture outputlayers.

According to an aspect of the disclosure, an apparatus may comprise: atleast one memory configured to store computer program code; and at leastone processor configured to access the at least one memory and operateaccording to the computer program code. According to an embodiment, thecomputer program code may comprise: receiving code configured to causethe at least one processor to receive a bitstream comprising compressedvideo/image data, wherein the bitstream has multiple layers; parsing orderiving code configured to cause the at least one processor to parse orderive, from the bitstream, an output layer set mode indicator in avideo parameter set (VPS); output layer signaling identifying codeconfigured to cause the at least one processor to identify output layerset signaling based on the output layer set mode indicator; pictureoutput layer identifying code configured to cause the at least oneprocessor to identify one or more picture output layers based on theidentified output layer set signaling; and decoding code configured tocause the at least one processor to: decode the identified one or morepicture output layers.

According to an embodiment, the computer program code may furthercomprise: display control code configured to cause the at least oneprocessor to control a display to display the one or more picture outputlayers.

According to an aspect of the disclosure, a method for signaling ofadaptive picture size in a video bitstream may comprise: receiving abitstream composed of compressed video/image data, wherein the bitstreamhas multiple layers; identifying a background region and one or moreforeground sub-pictures; determining whether a specific sub-pictureregion has been selected; and based on determining a specificsub-picture region has been selected: generating dequantized blockscorresponding to the selected sub-picture by a process including but notlimited to parsing the bitstream, decoding the entropy coded bitstreamand dequantizing the corresponding blocks.

The method may further comprise: decoding and displaying the backgroundregion, if the specific sub-picture region has not been selected.

The bitstream may include syntax elements that specify which layers maybe outputted at the decoder side.

The syntax elements may include a header of a picture containing avariable length, Exp-Golomb coded syntax element.

The method may further comprise: determining whether or not adaptiveresolution is in use for a picture or parts thereof based on signalingin a sequence parameter.

The determining whether or not adaptive resolution is in use for thepicture or the parts thereof may include: determining whether a firstsyntax element, which is a flag, indicates the use of adaptiveresolution.

The method may include the encoder instructing the decoder to use acertain reference picture size rather than implicitly assuming a size tobe an output picture size by using a flag that gates a conditionalpresence of reference picture dimensions.

The syntax elements may include a table of possible decoding picturewidth and heights.

According to an embodiment, a value in a Network Abstraction Layer (NAL)unit header may be used to indicate not only the temporal but also thespatial layer.

The value in the NAL unit header may be a Temporal Identifier (ID)field.

The method may further comprise: using existing Selected ForwardingUnits (SFU) created and optimized for temporal layer selected forwardingbased on the NAL unit header Temporal ID value without modification, forscalable environments.

The method may further comprise: mapping between the coded picture sizeand the temporal layer indicated by the temporal ID field in the NALunit header. \

The method may further comprise: receiving additional data with theencoded video, the additional data being included as part of the codedvideo sequence(s); and use the additional data to properly decode thedata and/or to more accurately reconstruct the original video data.

The additional data may be in the form of one or more of: temporal,spatial, or SNR enhancement layers, redundant slices, redundantpictures, or forward error correction codes.

According to an embodiment, a non-transitory computer-readable storagemedium storing instructions that, when executed, may cause a system ordevice comprising one or more processors to: receive a bitstreamcomposed of compressed video/image data, wherein the bitstream hasmultiple layers; identify a background region and one or more foregroundsub-pictures; determine whether a specific sub-picture region has beenselected; and based on determining a specific sub-picture region hasbeen selected: generate dequantized blocks corresponding to the selectedsub-picture by a process including but not limited to parsing thebitstream, decoding the entropy coded bitstream and dequantizing thecorresponding blocks.

According to an embodiment, an apparatus may comprise: at least onememory configured to store computer program code; and at least oneprocessor configured to access the at least one memory and operateaccording to the computer program code, the computer program codecomprising: receiving code configured to cause the at least oneprocessor to receive a bitstream composed of compressed video/imagedata, wherein the bitstream has multiple layers; identifying codeconfigured to cause the at least one processor to identify a backgroundregion and one or more foreground sub-pictures; determining codeconfigured to cause the at least one processor to determine whether aspecific sub-picture region has been selected; and generation codeconfigured to cause the at least one processor to: based on determininga specific sub-picture region has been selected: generate dequantizedblocks corresponding to the selected sub-picture by a process includingbut not limited to parsing the bitstream, decoding the entropy codedbitstream and dequantizing the corresponding blocks.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of options for signaling ARCparameters in accordance with prior art or an embodiment, as indicated.

FIG. 6 is an example of a syntax table in accordance with an embodiment.

FIG. 7 is a schematic illustration of a computer system in accordancewith an embodiment.

FIG. 8 is an example of prediction structure for scalability withadaptive resolution change.

FIG. 9 is an example of a syntax table in accordance with an embodiment.

FIG. 10 is a schematic illustration of a simplified block diagram ofparsing and decoding poc cycle per access unit and access unit countvalue.

FIG. 11 is a schematic illustration of a video bitstream structurecomprising multi-layered sub-pictures.

FIG. 12 is a schematic illustration of a display of the selectedsub-picture with an enhanced resolution.

FIG. 13 is a block diagram of the decoding and display process for avideo bitstream comprising multi-layered sub-pictures.

FIG. 14 is a schematic illustration of 360 video display with anenhancement layer of a sub-picture.

FIG. 15 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure.

FIG. 16 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure, with spatialscalability modality of local region.

FIG. 17 is an example of a syntax table for sub-picture layoutinformation

FIG. 18 is an example of a syntax table of SEI message for sub-picturelayout information.

FIG. 19 is an example of a syntax table to indicate output layers andprofile/tier/level information for each output layer set.

FIG. 20 is an example of a syntax table to indicate output layer mode onfor each output layer set.

FIG. 21 is an example of a syntax table to indicate the presentsubpicture of each layer for each output layer set.

FIG. 22 is an example of a syntax table of video parameter set RBSP.

FIG. 23 is an example of a syntax table to indicate the output layer setwith an output layer set mode indicator.

FIG. 24 is a block diagram of the decoding process for a bitstreamincluding for indicating the output layer set with an output layer setmode indicator.

FIGS. 25A-25C show information related to indicating the output layerset with an output layer set mode indicator.

DETAILED DESCRIPTION

When pictures are encoded into a bitstream that consists of multiplelayers with different qualities, the bitstream may have syntax elementsthat specify which layers may be outputted at decoder side. The set oflayers to be outputted is defined as an output layer set. In the latestvideo codec supporting multiple layers and scalabilities, one or moreoutput layer sets are signaled in a video parameter set. Those syntaxelements specifying output layer sets and their dependency,profile/tier/level and hypothetical decoder reference model parametersneed to be efficiently signaled in a parameter set.

Embodiments of the present disclosure address one or more problems ofthe related technology.

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110, 120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1 , although the terminals (110-140) are illustrated as a laptop110, a personal computer (PC) 120 and mobile terminals 130 and 140, theterminals (110-140) are not so limited and the terminals (110-140 maycorrespond to one or more or any combination of: servers, personalcomputers, mobile devices, tablets and smart phones. Embodiments of thepresent disclosure find application with laptop computers, tabletcomputers, media players and/or dedicated video conferencing equipment.The network (150) represents any number of networks that convey codedvideo data among the terminals (110-140), including for example wiredand/or wireless communication networks. The communication network (150)may exchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks (LANs), wide area networks (WANs) and/or the Internet. For thepurposes of the present discussion, the architecture and topology of thenetwork (150) may be immaterial to the operation of the presentdisclosure unless explained herein below.

FIG. 2 illustrates, as an example of an application of an embodiment ofthe disclosure, the placement of a video encoder and decoder in astreaming environment. The disclosure is may be equally applicable toother video enabled applications, including, for example, videoconferencing, digital television (TV), storing of compressed video ondigital media including compact disc (CD), digital versatile disc (DVD),memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, configuredto create, for example, an uncompressed video sample stream (202). Thatsample stream (202), depicted as a bold line in FIG. 2 to emphasize ahigh data volume when compared to encoded video bitstreams, can beprocessed by an encoder (203) coupled to the camera (201). The encoder(203) can include hardware, software, or a combination thereof to enableor implement aspects of the disclosed subject matter as described inmore detail below. The encoded video bitstream (204), depicted as a thinline in FIG. 2 to emphasize the lower data volume when compared to thesample stream (202), can be stored on a streaming server (205) forfuture use. One or more streaming clients (206, 208) can access thestreaming server (205) to retrieve copies (207, 209) of the encodedvideo bitstream (204). A client (206) can include a video decoder (210)which decodes the incoming copy of the encoded video bitstream (207) andcreates an outgoing video sample stream (211) that can be rendered on adisplay (212) or other rendering device. In some streaming systems, thevideo bitstreams (204, 207, 209) can be encoded according to certainvideo coding/compression standards. Examples of those standards includeITU-T Recommendation H.265. Under development is a video coding standardinformally known as Versatile Video Coding or VVC. The disclosed subjectmatter may be used in the context of VVC.

FIG. 3 may be a functional block diagram of a video decoder (210)according to an embodiment of the present disclosure.

A receiver (310) may receive one or more codec video sequences to bedecoded by the decoder (210); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (312), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (310) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (310) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween receiver (310) and entropy decoder/parser (320) (“parser”henceforth). When receiver (310) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer (315) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (315) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (210) may include an parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(210), and potentially information to control a rendering device such asa display (212) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 2 . The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments. The parser (320) may parse/entropy-decode thecoded video sequence received. The coding of the coded video sequencecan be in accordance with a video coding technology or standard, and canfollow principles well known to a person skilled in the art, includingvariable length coding, Huffman coding, arithmetic coding with orwithout context sensitivity, and so forth. The parser (320) may extractfrom the coded video sequence, a set of subgroup parameters for at leastone of the subgroups of pixels in the video decoder, based upon at leastone parameters corresponding to the group. Subgroups can include Groupsof Pictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units(CUs), blocks, Transform Units (TUs), Prediction Units (PUs) and soforth. The entropy decoder/parser may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). Subgroup control information may flow between the parser(320) and the multiple units.

Beyond the functional blocks already mentioned, decoder 210 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). It can output blockscomprising sample values, that can be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(358). The aggregator (355), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (352) has generatedto the output sample information as provided by the scaler/inversetransform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (321)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (356) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (212) as well as stored in the referencepicture memory (356) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picture(356) can become part of the reference picture buffer (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (parser) 320 may perform decoding operations accordingto a predetermined video compression technology that may be documentedin a standard, such as ITU-T Rec. H.265. The coded video sequence mayconform to a syntax specified by the video compression technology orstandard being used, in the sense that it adheres to the syntax of thevideo compression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (320) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 may be a functional block diagram of a video encoder (203)according to an embodiment of the present disclosure.

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focusses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (450). Controller (450) may control other functional units asdescribed below and is functionally coupled to these units. Parametersset by controller (450) may include rate control related parameters(picture skip, quantizer, lambda value of rate-distortion optimizationtechniques, . . . ), picture size, group of pictures (GOP) layout,maximum motion vector search range, and so forth. A person skilled inthe art can readily identify other functions of controller (450) as theymay pertain to video encoder (203) optimized for a certain systemdesign.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder (203)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (433) embedded in the encoder (203) that reconstructs thesymbols to create the sample data a (remote) decoder also would create(as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (434). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3 . Briefly referring also to FIG. 3 , however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (445) and parser (320) can be lossless, theentropy decoding parts of decoder (210), including channel (312),receiver (310), buffer (315), and parser (320) may not be fullyimplemented in local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focusses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

As part of its operation, the source coder (203) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(203), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams/sources.

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Before describing certain aspects of the disclosed subject matter inmore detail, a few terms need to be introduced that will be referred toin the remainder of this description.

Sub-Picture henceforth refers to an, in some cases, rectangulararrangement of samples, blocks, macroblocks, coding units, or similarentities that are semantically grouped, and that may be independentlycoded in changed resolution. One or more sub-pictures may for a picture.One or more coded sub-pictures may form a coded picture. One or moresub-pictures may be assembled into a picture, and one or more subpictures may be extracted from a picture. In certain environments, oneor more coded sub-pictures may be assembled in the compressed domainwithout transcoding to the sample level into a coded picture, and in thesame or certain other cases, one or more coded sub-pictures may beextracted from a coded picture in the compressed domain.

Adaptive Resolution Change (ARC) henceforth refers to mechanisms thatallow the change of resolution of a picture or sub-picture within acoded video sequence, by the means of, for example, reference pictureresampling. ARC parameters henceforth refer to the control informationrequired to perform adaptive resolution change, which may include, forexample, filter parameters, scaling factors, resolutions of outputand/or reference pictures, various control flags, and so forth.

The above description is focused on coding and decoding a single,semantically independent coded video picture according to variousembodiments. Before describing the implication of coding/decoding ofmultiple sub pictures with independent ARC parameters and its impliedadditional complexity, options for signaling ARC parameters may bedescribed.

Referring to FIG. 5 , shown are several novel options for signaling ARCparameters. As noted with each of the options, they have certainadvantages and certain disadvantages from a coding efficiency,complexity, and architecture viewpoint. A video coding standard ortechnology may choose one or more of these options, or options knownfrom previous art, for signaling ARC parameters. The options may not bemutually exclusive, and conceivably may be interchanged based onapplication needs, standards technology involved, or encoder's choice.

Classes of ARC parameters may include:

-   -   up/downsample factors, separate or combined in X and Y        dimension;    -   up/downsample factors, with an addition of a temporal dimension,        indicating constant speed zoom in/out for a given number of        pictures;    -   Either of the above two may involve the coding of one or more        presumably short syntax elements that may point into a table        containing the factor(s);    -   resolution, in X or Y dimension, in units of samples, blocks,        macroblocks, CUs, or any other suitable granularity, of the        input picture, output picture, reference picture, coded picture,        combined or separately. If there are more than one resolution        (such as, for example, one for input picture, one for reference        picture) then, in certain cases, one set of values may be        inferred to from another set of values. Such could be gated, for        example, by the use of flags. For a more detailed example, see        below;    -   “warping” coordinates akin those used in H.263 Annex P, again in        a suitable granularity as described above. H.263 Annex P defines        one efficient way to code such warping coordinates, but other,        potentially more efficient ways could conceivably also be        devised. For example, the variable length reversible,        “Huffman”-style coding of warping coordinates of Annex P could        be replaced by a suitable length binary coding, where the length        of the binary code word could, for example, be derived from a        maximum picture size, possibly multiplied by a certain factor        and offset by a certain value, so to allow for “warping” outside        of the maximum picture size's boundaries; and    -   up or downsample filter parameters. In the easiest case, there        may be only a single filter for up and/or downsampling. However,        in certain cases, it can be advantageous to allow more        flexibility in filter design, and that may require to signaling        of filter parameters. Such parameters may be selected through an        index in a list of possible filter designs, the filter may be        fully specified (for example through a list of filter        coefficients, using suitable entropy coding techniques), the        filter may be implicitly selected through up/downsample ratios        according which in turn are signaled according to any of the        mechanisms mentioned above, and so forth.

Henceforth, the description assumes the coding of a finite set ofup/downsample factors (the same factor to be used in both X and Ydimension), indicated through a codeword. That codeword canadvantageously be variable length coded, for example using theExt-Golomb code common for certain syntax elements in video codingspecifications such as H.264 and H.265.

One suitable mapping of values to up/downsample factors can, forexample, be according to the following table:

TABLE 1 Codeword Ext-Golomb Code Original/Target resolution 0 1 1/1 1010 1/1.5 (upscale by 50%) 2 011 1.5/1 (downscale by 50%) 3 00100 1/2(upscale by 100%) 4 00101 2/1 (downscale by 100%)

Many similar mappings could be devised according to the needs of anapplication and the capabilities of the up and downscale mechanismsavailable in a video compression technology or standard. The table couldbe extended to more values. Values may also be represented by entropycoding mechanisms other than Ext-Golomb codes, for example using binarycoding. That may have certain advantages when the resampling factorswere of interest outside the video processing engines (encoder anddecoder foremost) themselves, for example by Mobile ad hoc networks(MANETs). It should be noted that, for the (presumably) most common casewhere no resolution change is required, an Ext-Golomb code can be chosenthat is short; in the table above, only a single bit. That can have acoding efficiency advantage over using binary codes for the most commoncase.

The number of entries in the table, as well as their semantics may befully or partially configurable. For example, the basic outline of thetable may be conveyed in a “high” parameter set such as a sequence ordecoder parameter set. Alternatively or in addition, one or more suchtables may be defined in a video coding technology or standard, and maybe selected through for example a decoder or sequence parameter set.

Henceforth, we describe how an upsample/downsample factor (ARCinformation), coded as described above, may be included in a videocoding technology or standard syntax. Similar considerations may applyto one, or a few, codewords controlling up/downsample filters. See belowfor a discussion when comparatively large amounts of data are requiredfor a filter or other data structures.

H.263 Annex P includes the ARC information 502 in the form of fourwarping coordinates into the picture header 501, specifically in theH.263 PLUSPTYPE (503) header extension. This can be a sensible designchoice when a) there is a picture header available, and b) frequentchanges of the ARC information are expected. However, the overhead whenusing H.263-style signaling can be quite high, and scaling factors maynot pertain among picture boundaries as picture header can be oftransient nature.

JVCET-M135-v1, cited above, includes the ARC reference information (505)(an index) located in a picture parameter set (504), indexing a table(506) including target resolutions that in turn is located inside asequence parameter set (SPS) (507). The placement of the possibleresolution in a table (506) in the sequence parameter set (507) can,according to verbal statements made by the authors, be justified byusing the SPS as an interoperability negotiation point during capabilityexchange. Resolution can change, within the limits set by the values inthe table (506) from picture to picture by referencing the appropriatepicture parameter set (504).

Referring back to FIG. 5 , the following additional options may exist toconvey ARC information in a video bitstream. Each of those options hascertain advantages over existing art as described above. The options maybe simultaneously present in the same video coding technology orstandard.

In an embodiment, ARC information (509) such as a resampling (zoom)factor may be present in a slice header, group of block (GOB) header,tile header, or tile group header (tile group header henceforth) (508).This can be adequate if the ARC information is small, such as a singlevariable length ue(v) or fixed length codeword of a few bits, forexample as shown above. Having the ARC information in a tile groupheader directly has the additional advantage of the ARC information maybe applicable to a sub picture represented by, for example, that tilegroup, rather than the whole picture. See also below. In addition, evenif the video compression technology or standard envisions only wholepicture adaptive resolution changes (in contrast to, for example, tilegroup based adaptive resolution changes), putting the ARC informationinto the tile group header vis a vis putting it into an H.263-stylepicture header has certain advantages from an error resilienceviewpoint.

In the same or another embodiment, the ARC information (512) itself maybe present in an appropriate parameter set (511) such as, for example, apicture parameter set (PPS), header parameter set, tile parameter set,adaptation parameter set, and so forth (Adaptation parameter setdepicted). The scope of that parameter set can advantageously be nolarger than a picture, for example a tile group. The use of the ARCinformation is implicit through the activation of the relevant parameterset. For example, when a video coding technology or standardcontemplates only picture-based ARC, then a picture parameter set orequivalent may be appropriate.

In the same or another embodiment, ARC reference information (513) maybe present in a Tile Group header (514) or a similar data structure.That reference information (513) can refer to a subset of ARCinformation (515) available in a parameter set (516) with a scope beyonda single picture, for example a sequence parameter set, or decoderparameter set.

The additional level of indirection implied activation of a PPS from atile group header, PPS, SPS, as used in JVET-M0135-v1 appears to beunnecessary, as picture parameter sets, just as sequence parameter sets,can (and have in certain standards such as RFC3984) be used forcapability negotiation or announcements. If, however, the ARCinformation should be applicable to a sub picture represented, forexample, by a tile groups also, a parameter set with an activation scopelimited to a tile group, such as the Adaptation Parameter set or aHeader Parameter Set may be the better choice. Also, if the ARCinformation is of more than a negligible size—for example containsfilter control information such as numerous filter coefficients—then aparameter set may be a better choice than using a header (508) directlyfrom a coding efficiency viewpoint, as those settings may be reusable byfuture pictures or sub-pictures by referencing the same parameter set.

When using the sequence parameter set or another higher parameter setwith a scope spanning multiple pictures, certain considerations mayapply:

1. The parameter set to store the ARC information table (516) can, insome cases, be the sequence parameter set, but in other casesadvantageously be the decoder parameter set. The decoder parameter setcan have an activation scope of multiple CVSs, namely the coded videostream, i.e. all coded video bits from session start until sessionteardown. Such a scope may be more appropriate because possible ARCfactors may be a decoder feature, possibly implemented in hardware, andhardware features tend not to change with any CVS (which in at leastsome entertainment systems is a Group of Pictures, one second or less inlength). That said, putting the table into the sequence parameter set isexpressly included in the placement options described herein, inparticular in conjunction with point 2 below.

2. The ARC reference information (513) may advantageously be placeddirectly into the picture/slice tile/GOB/tile group header (tile groupheader henceforth) (514) rather than into the picture parameter set asin JVCET-M0135-v1. The reason is as follows: when an encoder wants tochange a single value in a picture parameter set, such as for examplethe ARC reference information, then it has to create a new PPS andreference that new PPS. Assume that only the ARC reference informationchanges, but other information such as, for example, the quantizationmatrix information in the PPS stays. Such information can be ofsubstantial size, and would need to be retransmitted to make the new PPScomplete.

As the ARC reference information may be a single codeword, such as theindex into the table (513) and that would be the only value thatchanges, it would be cumbersome and wasteful to retransmit all the, forexample, quantization matrix information. Insofar, can be considerablybetter from a coding efficiency viewpoint to avoid the indirectionthrough the PPS, as proposed in JVET-M0135-v1. Similarly, putting theARC reference information into the PPS has the additional disadvantagethat the ARC information referenced by the ARC reference information(513) necessarily needs to apply to the whole picture and not to asub-picture, as the scope of a picture parameter set activation is apicture.

In the same or another embodiment, the signaling of ARC parameters canfollow a detailed example as outlined in FIG. 6 . FIG. 6 depicts syntaxdiagrams in a representation as used in video coding standards since atleast 1993. The notation of such syntax diagrams roughly follows C-styleprogramming. In FIG. 6 , lines in boldface indicate syntax elementspresent in the bitstream, lines without boldface often indicate controlflow or the setting of variables.

A tile group header (601) as an exemplary syntax structure of a headerapplicable to a (possibly rectangular) part of a picture canconditionally contain, a variable length, Exp-Golomb coded syntaxelement dec_pic_size_idx (602) (depicted in boldface). The presence ofthis syntax element in the tile group header can be gated on the use ofadaptive resolution (603)—here, the value of a flag not depicted inboldface, which means that flag is present in the bitstream at the pointwhere it occurs in the syntax diagram.

Whether or not adaptive resolution is in use for this picture or partsthereof can be signaled in any high level syntax structure inside oroutside the bitstream. In the example shown in FIG. 6 , it is signaledin the sequence parameter set as outlined below.

Still referring to FIG. 6 , shown is also an excerpt of a sequenceparameter set (610). The first syntax element shown isadaptive_pic_resolution_change_flag (611). When true, that flag canindicate the use of adaptive resolution which, in turn may requirecertain control information. In the example, such control information isconditionally present based on the value of the flag based on the if( )statement in the parameter set (612) and the tile group header (601).

When adaptive resolution is in use, in this example, coded is an outputresolution in units of samples (613). The numeral 613 refers to bothoutput_pic_width_in_luma_samples and output_pic_height_in_luma_samples,which together can define the resolution of the output picture.Elsewhere in a video coding technology or standard, certain restrictionsto either value can be defined. For example, a level definition maylimit the number of total output samples, which could be the product ofthe value of those two syntax elements. Also, certain video codingtechnologies or standards, or external technologies or standards suchas, for example, system standards, may limit the numbering range (forexample, one or both dimensions must be divisible by a power of 2number), or the aspect ratio (for example, the width and height must bein a relation such as 4:3 or 16:9). Such restrictions may be introducedto facilitate hardware implementations or for other reasons, and arewell known in the art.

In certain applications, the encoder may instruct the decoder to use acertain reference picture size rather than implicitly assume a size tobe the output picture size. In this example, the syntax elementreference_pic_size_present_flag (614) gates the conditional presence ofreference picture dimensions (615) (again, the numeral refers to bothwidth and height).

Finally, shown in FIG. 6 , is a table of possible decoding picture widthand heights. Such a table can be expressed, for example, by a tableindication (num_dec_pic_size_in_luma_samples_minus1) (616). The “minus1”can refer to the interpretation of the value of that syntax element. Forexample, if the coded value is zero, one table entry is present. If thevalue is five, six table entries are present. For each “line” in thetable, decoded picture width and height are then included in the syntax(617).

The table entries presented (617) can be indexed using the syntaxelement dec_pic_size_idx (602) in the tile group header, therebyallowing different decoded sizes—in effect, zoom factors—per tile group.

Certain video coding technologies or standards, for example VP9, supportspatial scalability by implementing certain forms of reference pictureresampling (signaled quite differently from the disclosed subjectmatter) in conjunction with temporal scalability, so to enable spatialscalability. In particular, certain reference pictures may be upsampledusing ARC-style technologies to a higher resolution to form the base ofa spatial enhancement layer. Those upsampled pictures could be refined,using normal prediction mechanisms at the high resolution, so to adddetail.

The disclosed subject matter can be used in such an environment. Incertain cases, in the same or another embodiment, a value in the NetworkAbstraction Layer (NAL) unit header, for example the Temporal Identifier(ID) field, can be used to indicate not only the temporal but also thespatial layer. Doing so has certain advantages for certain systemdesigns; for example, existing Selected Forwarding Units (SFU) createdand optimized for temporal layer selected forwarding based on the NALunit header Temporal ID value can be used without modification, forscalable environments. In order to enable that, there may be arequirement for a mapping between the coded picture size and thetemporal layer is indicated by the temporal ID field in the NAL unitheader.

In some video coding technologies, an Access Unit (AU) can refer tocoded picture(s), slice(s), tile(s), NAL Unit(s), and so forth, thatwere captured and composed into a the respective picture/slice/tile/NALunit bitstream at a given instance in time. That instance in time can bethe composition time.

In HEVC, and certain other video coding technologies, a picture ordercount (POC) value can be used for indicating a selected referencepicture among multiple reference picture stored in a decoded picturebuffer (DPB). When an access unit (AU) comprises one or more pictures,slices, or tiles, each picture, slice, or tile belonging to the same AUmay carry the same POC value, from which it can be derived that theywere created from content of the same composition time. In other words,in a scenario where two pictures/slices/tiles carry the same given POCvalue, that can be indicative of the two picture/slice/tile belonging tothe same AU and having the same composition time. Conversely, twopictures/tiles/slices having different POC values can indicate thosepictures/slices/tiles belonging to different AUs and having differentcomposition times.

In an embodiment of the disclosed subject matter, aforementioned rigidrelationship can be relaxed in that an access unit can comprisepictures, slices, or tiles with different POC values. By allowingdifferent POC values within an AU, it becomes possible to use the POCvalue to identify potentially independently decodablepictures/slices/tiles with identical presentation time. That, in turn,can enable support of multiple scalable layers without a change ofreference picture selection signaling (e.g. reference picture setsignaling or reference picture list signaling), as described in moredetail below.

It is, however, still desirable to be able to identify the AU apicture/slice/tile belongs to, with respect to otherpicture/slices/tiles having different POC values, from the POC valuealone. This can be achieved, as described below.

In the same or other embodiments, an access unit count (AUC) may besignaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The value of AUC may be used to identify which NAL units,pictures, slices, or tiles belong to a given AU. The value of AUC may becorresponding to a distinct composition time instance. The AUC value maybe equal to a multiple of the POC value. By dividing the POC value by aninteger value, the AUC value may be calculated. In certain cases,division operations can place a certain burden on decoderimplementations. In such cases, small restrictions in the numberingspace of the AUC values may allow to substitute the division operationby shift operations. For example, the AUC value may be equal to a MostSignificant Bit (MSB) value of the POC value range.

In the same embodiment, a value of POC cycle per AU (poc_cycle_au) maybe signaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The poc_cycle_au may indicate how many different andconsecutive POC values can be associated with the same AU. For example,if the value of poc_cycle_au is equal to 4, the pictures, slices ortiles with the POC value equal to 0-3, inclusive, are associated withthe AU with AUC value equal to 0, and the pictures, slices or tiles withPOC value equal to 4-7, inclusive, are associated with the AU with AUCvalue equal to 1. Hence, the value of AUC may be inferred by dividingthe POC value by the value of poc_cycle_au.

In the same or another embodiment, the value of poc_cyle_au may bederived from information, located for example in the video parameter set(VPS), that identifies the number of spatial or SNR layers in a codedvideo sequence. Such a possible relationship is briefly described below.While the derivation as described above may save a few bits in the VPSand hence may improve coding efficiency, it can be advantageous toexplicitly code poc_cycle_au in an appropriate high level syntaxstructure hierarchically below the video parameter set, so to be able tominimize poc_cycle_au for a given small part of a bitstream such as apicture. This optimization may save more bits than can be saved throughthe derivation process above because POC values (and/or values of syntaxelements indirectly referring to POC) may be coded in low level syntaxstructures.

In the same or another embodiment, FIG. 9 shows an example of syntaxtables to signal the syntax element of vps_poc_cycle_au in VPS (or SPS),which indicates the poc_cycle_au used for all picture/slices in a codedvideo sequence, and the syntax element of slice_poc_cycle_au, whichindicates the poc_cycle_au of the current slice, in slice header. If thePOC value increases uniformly per AU, vps_contant_poc_cycle_per_au inVPS is set equal to 1 and vps_poc_cycle_au is signaled in VPS. In thiscase, slice_poc_cycle_au is not explicitly signaled, and the value ofAUC for each AU is calculated by dividing the value of POC byvps_poc_cycle_au. If the POC value does not increase uniformly per AU,vps_contant_poc_cycle_per_au in VPS is set equal to 0. In this case,vps_access_unit_cnt is not signaled, while slice_access_unit_cnt issignaled in slice header for each slice or picture. Each slice orpicture may have a different value of slice_access_unit_cnt. The valueof AUC for each AU is calculated by dividing the value of POC byslice_poc_cycle_au. FIG. 10 shows a block diagram illustrating therelevant work flow.

In the same or other embodiments, even though the value of POC of apicture, slice, or tile may be different, the picture, slice, or tilecorresponding to an AU with the same AUC value may be associated withthe same decoding or output time instance. Hence, without anyinter-parsing/decoding dependency across pictures, slices or tiles inthe same AU, all or subset of pictures, slices or tiles associated withthe same AU may be decoded in parallel, and may be outputted at the sametime instance.

In the same or other embodiments, even though the value of POC of apicture, slice, or tile may be different, the picture, slice, or tilecorresponding to an AU with the same AUC value may be associated withthe same composition/display time instance. When the composition time iscontained in a container format, even though pictures correspond todifferent AUs, if the pictures have the same composition time, thepictures can be displayed at the same time instance.

In the same or other embodiments, each picture, slice, or tile may havethe same temporal identifier (temporal_id) in the same AU. All or subsetof pictures, slices or tiles corresponding to a time instance may beassociated with the same temporal sub-layer. In the same or otherembodiments, each picture, slice, or tile may have the same or adifferent spatial layer id (layer_id) in the same AU. All or subset ofpictures, slices or tiles corresponding to a time instance may beassociated with the same or a different spatial layer.

FIG. 8 shows an example of a video sequence structure with combinationof temporal_id, layer_id, POC and AUC values with adaptive resolutionchange. In this example, a picture, slice or tile in the first AU withAUC=0 may have temporal_id=0 and layer_id=0 or 1, while a picture, sliceor tile in the second AU with AUC=1 may have temporal_id=1 andlayer_id=0 or 1, respectively. The value of POC is increased by 1 perpicture regardless of the values of temporal_id and layer_id. In thisexample, the value of poc_cycle_au can be equal to 2. Preferably, thevalue of poc_cycle_au may be set equal to the number of (spatialscalability) layers. In this example, hence, the value of POC isincreased by 2, while the value of AUC is increased by 1.

In the above embodiments, all or sub-set of inter-picture or inter-layerprediction structure and reference picture indication may be supportedby using the existing reference picture set (RPS) signaling in HEVC orthe reference picture list (RPL) signaling. In RPS or RPL, the selectedreference picture is indicated by signaling the value of POC or thedelta value of POC between the current picture and the selectedreference picture. For the disclosed subject matter, the RPS and RPL canbe used to indicate the inter-picture or inter-layer predictionstructure without change of signaling, but with the followingrestrictions. If the value of temporal_id of a reference picture isgreater than the value of temporal_id current picture, the currentpicture may not use the reference picture for motion compensation orother predictions. If the value of layer_id of a reference picture isgreater than the value of layer_id current picture, the current picturemay not use the reference picture for motion compensation or otherpredictions.

In the same and other embodiments, the motion vector scaling based onPOC difference for temporal motion vector prediction may be disabledacross multiple pictures within an access unit. Hence, although eachpicture may have a different POC value within an access unit, the motionvector is not scaled and used for temporal motion vector predictionwithin an access unit. This is because a reference picture with adifferent POC in the same AU is considered a reference picture havingthe same time instance. Therefore, in the embodiment, the motion vectorscaling function may return 1, when the reference picture belongs to theAU associated with the current picture.

In the same and other embodiments, the motion vector scaling based onPOC difference for temporal motion vector prediction may be optionallydisabled across multiple pictures, when the spatial resolution of thereference picture is different from the spatial resolution of thecurrent picture. When the motion vector scaling is allowed, the motionvector is scaled based on both POC difference and the spatial resolutionratio between the current picture and the reference picture.

In the same or another embodiment, the motion vector may be scaled basedon AUC difference instead of POC difference, for temporal motion vectorprediction, especially when the poc_cycle_au has non-uniform value (whenvps_contant_poc_cycle_per_au==0). Otherwise (whenvps_contant_poc_cycle_per_au==1), the motion vector scaling based on AUCdifference may be identical to the motion vector scaling based on POCdifference.

In the same or another embodiment, when the motion vector is scaledbased on AUC difference, the reference motion vector in the same AU(with the same AUC value) with the current picture is not scaled basedon AUC difference and used for motion vector prediction without scalingor with scaling based on spatial resolution ratio between the currentpicture and the reference picture.

In the same and other embodiments, the AUC value is used for identifyingthe boundary of AU and used for hypothetical reference decoder (HRD)operation, which needs input and output timing with AU granularity. Inmost cases, the decoded picture with the highest layer in an AU may beoutputted for display. The AUC value and the layer_id value can be usedfor identifying the output picture.

In an embodiment, a picture may consist of one or more sub-pictures.Each sub-picture may cover a local region or the entire region of thepicture. The region supported by a sub-picture may or may not beoverlapped with the region supported by another sub-picture. The regioncomposed by one or more sub-pictures may or may not cover the entireregion of a picture. If a picture consists of a sub-picture, the regionsupported by the sub-picture is identical to the region supported by thepicture.

In the same embodiment, a sub-picture may be coded by a coding methodsimilar to the coding method used for the coded picture. A sub-picturemay be independently coded or may be coded dependent on anothersub-picture or a coded picture. A sub-picture may or may not have anyparsing dependency from another sub-picture or a coded picture.

In the same embodiment, a coded sub-picture may be contained in one ormore layers. A coded sub-picture in a layer may have a different spatialresolution. The original sub-picture may be spatially re-sampled(up-sampled or down-sampled), coded with different spatial resolutionparameters, and contained in a bitstream corresponding to a layer.

In the same or another embodiment, a sub-picture with (W, H), where Windicates the width of the sub-picture and H indicates the height of thesub-picture, respectively, may be coded and contained in the codedbitstream corresponding to layer 0, while the up-sampled (ordown-sampled) sub-picture from the sub-picture with the original spatialresolution, with (W*S_(w,k), H*S_(h,k)), may be coded and contained inthe coded bitstream corresponding to layer k, where S_(w,k), S_(h,k)indicate the resampling ratios, horizontally and vertically. If thevalues of S_(w,k), S_(h,k) are greater than 1, the resampling is equalto the up-sampling. Whereas, if the values of S_(w,k), S_(h,k) aresmaller than 1, the resampling is equal to the down-sampling.

In the same or another embodiment, a coded sub-picture in a layer mayhave a different visual quality from that of the coded sub-picture inanother layer in the same sub-picture or different subpicture. Forexample, sub-picture i in a layer, n, is coded with the quantizationparameter, Q_(i,n), while a sub-picture j in a layer, m, is coded withthe quantization parameter, Q_(j,m).

In the same or another embodiment, a coded sub-picture in a layer may beindependently decodable, without any parsing or decoding dependency froma coded sub-picture in another layer of the same local region. Thesub-picture layer, which can be independently decodable withoutreferencing another sub-picture layer of the same local region, is theindependent sub-picture layer. A coded sub-picture in the independentsub-picture layer may or may not have a decoding or parsing dependencyfrom a previously coded sub-picture in the same sub-picture layer, butthe coded sub-picture may not have any dependency from a coded picturein another sub-picture layer.

In the same or another embodiment, a coded sub-picture in a layer may bedependently decodable, with any parsing or decoding dependency from acoded sub-picture in another layer of the same local region. Thesub-picture layer, which can be dependently decodable with referencinganother sub-picture layer of the same local region, is the dependentsub-picture layer. A coded sub-picture in the dependent sub-picture mayreference a coded sub-picture belonging to the same sub-picture, apreviously coded sub-picture in the same sub-picture layer, or bothreference sub-pictures.

In the same or another embodiment, a coded sub-picture consists of oneor more independent sub-picture layers and one or more dependentsub-picture layers. However, at least one independent sub-picture layermay be present for a coded sub-picture. The independent sub-picturelayer may have the value of the layer identifier (layer_id), which maybe present in NAL unit header or another high-level syntax structure,equal to 0. The sub-picture layer with the layer_id equal to 0 is thebase sub-picture layer.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures and one background sub-picture. The regionsupported by a background sub-picture may be equal to the region of thepicture. The region supported by a foreground sub-picture may beoverlapped with the region supported by a background sub-picture. Thebackground sub-picture may be a base sub-picture layer, while theforeground sub-picture may be a non-base (enhancement) sub-picturelayer. One or more non-base sub-picture layer may reference the samebase layer for decoding. Each non-base sub-picture layer with layer_idequal to a may reference a non-base sub-picture layer with layer_idequal to b, where a is greater than b.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Eachsub-picture may have its own base sub-picture layer and one or morenon-base (enhancement) layers. Each base sub-picture layer may bereferenced by one or more non-base sub-picture layers. Each non-basesub-picture layer with layer_id equal to a may reference a non-basesub-picture layer with layer_id equal to b, where a is greater than b.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Eachcoded sub-picture in a (base or non-base) sub-picture layer may bereferenced by one or more non-base layer sub-pictures belonging to thesame sub-picture and one or more non-base layer sub-pictures, which arenot belonging to the same sub-picture.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Asub-picture in a layer a may be further partitioned into multiplesub-pictures in the same layer. One or more coded sub-pictures in alayer b may reference the partitioned sub-picture in a layer a.

In the same or another embodiment, a coded video sequence (CVS) may be agroup of the coded pictures. The CVS may consist of one or more codedsub-picture sequences (CSPS), where the CSPS may be a group of codedsub-pictures covering the same local region of the picture. A CSPS mayhave the same or a different temporal resolution than that of the codedvideo sequence.

In the same or another embodiment, a CSPS may be coded and contained inone or more layers. A CSPS may consist of one or more CSPS layers.Decoding one or more CSPS layers corresponding to a CSPS may reconstructa sequence of sub-pictures corresponding to the same local region.

In the same or another embodiment, the number of CSPS layerscorresponding to a CSPS may be identical to or different from the numberof CSPS layers corresponding to another CSPS.

In the same or another embodiment, a CSPS layer may have a differenttemporal resolution (e.g. frame rate) from another CSPS layer. Theoriginal (uncompressed) sub-picture sequence may be temporallyre-sampled (up-sampled or down-sampled), coded with different temporalresolution parameters, and contained in a bitstream corresponding to alayer.

In the same or another embodiment, a sub-picture sequence with the framerate, F, may be coded and contained in the coded bitstream correspondingto layer 0, while the temporally up-sampled (or down-sampled)sub-picture sequence from the original sub-picture sequence, withF*S_(t,k), may be coded and contained in the coded bitstreamcorresponding to layer k, where S_(t,k) indicates the temporal samplingratio for layer k. If the value of S_(t,k) is greater than 1, thetemporal resampling process is equal to the frame rate up conversion.Whereas, if the value of S_(t,k) is smaller than 1, the temporalresampling process is equal to the frame rate down conversion.

In the same or another embodiment, when a sub-picture with a CSPS layera is reference by a sub-picture with a CSPS layer b for motioncompensation or any inter-layer prediction, if the spatial resolution ofthe CSPS layer a is different from the spatial resolution of the CSPSlayer b, decoded pixels in the CSPS layer a are resampled and used forreference. The resampling process may need an up-sampling filtering or adown-sampling filtering.

FIG. 11 shows an example video stream including a background video CSPSwith layer_id equal to 0 and multiple foreground CSPS layers. While acoded sub-picture may consist of one or more CSPS layers, a backgroundregion, which does not belong to any foreground CSPS layer, may consistof a base layer. The base layer may contain a background region andforeground regions, while an enhancement CSPS layer may contain aforeground region. An enhancement CSPS layer may have a better visualquality than the base layer, at the same region. The enhancement CSPSlayer may reference the reconstructed pixels and the motion vectors ofthe base layer, corresponding to the same region.

In the same or another embodiment, the video bitstream corresponding toa base layer is contained in a track, while the CSPS layerscorresponding to each sub-picture are contained in a separated track, ina video file.

In the same or another embodiment, the video bitstream corresponding toa base layer is contained in a track, while CSPS layers with the samelayer_id are contained in a separated track. In this example, a trackcorresponding to a layer k includes CSPS layers corresponding to thelayer k, only.

In the same or another embodiment, each CSPS layer of each sub-pictureis stored in a separate track. Each track may or may not have anyparsing or decoding dependency from one or more other tracks.

In the same or another embodiment, each track may contain bitstreamscorresponding to layer i to layer j of CSPS layers of all or a subset ofsub-pictures, where 0<i=<j=<k, k being the highest layer of CSPS.

In the same or another embodiment, a picture consists of one or moreassociated media data including depth map, alpha map, 3D geometry data,occupancy map, etc. Such associated timed media data can be divided toone or multiple data sub-stream each of which corresponding to onesub-picture.

In the same or another embodiment, FIG. 12 shows an example of a videoconference based on the multi-layered sub-picture method. In a videostream, one base layer video bitstream corresponding to the backgroundpicture and one or more enhancement layer video bitstreams correspondingto foreground sub-pictures are contained. Each enhancement layer videobitstream may correspond to a CSPS layer. In a display, the picturecorresponding to the base layer is displayed by default. It contains oneor more user's picture in a picture (PIP). When a specific user isselected by a client's control, the enhancement CSPS layer correspondingto the selected user is decoded and displayed with the enhanced qualityor spatial resolution.

FIG. 13 shows a block diagram of the decoding and display process for avideo bitstream comprising multi-layered sub-pictures according to anembodiment. For example, the process may include one or more of thefollowing operations. For example, in Operation 1301, decoding of thevideo bitstream with multi-layers may occur. Operation 1302 may includeidentifying the background region and one or more foregroundsub-pictures. Operation 1303 may include determining whether a specificsub-picture region has been selected. Operation 1304 may includedecoding and displaying the enhanced sub-picture if a specificsub-picture region has been selected (i.e., 1303=Yes). Operation 1305may include decoding and displaying the background region, if thespecific sub-picture region has not been selected (i.e., 1303=No).

In the same or another embodiment, a network middle box (such as arouter) may select a subset of layers to send to a user depending on itsbandwidth. The picture/subpicture organization may be used for bandwidthadaptation. For instance, if the user doesn't have the bandwidth, therouter may strip layers or select some subpictures due to theirimportance or based on user setup and this can be done dynamically toadopt to bandwidth.

FIG. 14 shows a use case of 360 video. When a spherical 360 picture isprojected onto a planar picture, the projection 360 picture may bepartitioned into multiple sub-pictures as a base layer. An enhancementlayer of a specific sub-picture may be coded and transmitted to aclient. A decoder may be able to decode both the base layer includingall sub-pictures and an enhancement layer of a selected sub-picture.When the current viewport is identical to the selected sub-picture, thedisplayed picture may have a higher quality with the decoded sub-picturewith the enhancement layer. Otherwise, the decoded picture with the baselayer can be displayed, with a low quality.

In the same or another embodiment, any layout information for displaymay be present in a file, as supplementary information (such as SEImessage or metadata). One or more decoded sub-pictures may be relocatedand displayed depending on the signaled layout information. The layoutinformation may be signaled by a streaming server or a broadcaster, ormay be regenerated by a network entity or a cloud server, or may bedetermined by a user's customized setting.

In an embodiment, when an input picture is divided into one or more(rectangular) sub-region(s), each sub-region may be coded as anindependent layer. Each independent layer corresponding to a localregion may have a unique layer_id value. For each independent layer, thesub-picture size and location information may be signaled. For example,picture size (width, height), the offset information of the left-topcorner (x_offset, y_offset). FIG. 15 shows an example of the layout ofdivided sub-pictures, its sub-picture size and position information andits corresponding picture prediction structure. The layout informationincluding the sub-picture size(s) and the sub-picture position(s) may besignaled in a high-level syntax structure, such as parameter set(s),header of slice or tile group, or SEI message.

In the same embodiment, each sub-picture corresponding to an independentlayer may have its unique POC value within an AU. When a referencepicture among pictures stored in DPB is indicated by using syntaxelement(s) in RPS or RPL structure, the POC value(s) of each sub-picturecorresponding to a layer may be used.

In the same or another embodiment, in order to indicate the(inter-layer) prediction structure, the layer_id may not be used and thePOC (delta) value may be used.

In the same embodiment, a sub-picture with a POC vale equal to Ncorresponding to a layer (or a local region) may or may not be used as areference picture of a sub-picture with a POC value equal to N+K,corresponding to the same layer (or the same local region) for motioncompensated prediction. In most cases, the value of the number K may beequal to the maximum number of (independent) layers, which may beidentical to the number of sub-regions.

In the same or another embodiment, FIG. 16 shows the extended case ofFIG. 15 . When an input picture is divided into multiple (e.g. four)sub-regions, each local region may be coded with one or more layers. Inthe case, the number of independent layers may be equal to the number ofsub-regions, and one or more layers may correspond to a sub-region.Thus, each sub-region may be coded with one or more independent layer(s)and zero or more dependent layer(s).

In the same embodiment, in FIG. 16 , the input picture may be dividedinto four sub-regions. The right-top sub-region may be coded as twolayers, which are layer 1 and layer 4, while the right-bottom sub-regionmay be coded as two layers, which are layer 3 and layer 5. In this case,the layer 4 may reference the layer 1 for motion compensated prediction,while the layer 5 may reference the layer 3 for motion compensation.

In the same or another embodiment, in-loop filtering (such as deblockingfiltering, adaptive in-loop filtering, reshaper, bilateral filtering orany deep-learning based filtering) across layer boundary may be(optionally) disabled.

In the same or another embodiment, motion compensated prediction orintra-block copy across layer boundary may be (optionally) disabled.

In the same or another embodiment, boundary padding for motioncompensated prediction or in-loop filtering at the boundary ofsub-picture may be processed optionally. A flag indicating whether theboundary padding is processed or not may be signaled in a high-levelsyntax structure, such as parameter set(s) (VPS, SPS, PPS, or APS),slice or tile group header, or SEI message.

In the same or another embodiment, the layout information ofsub-region(s) (or sub-picture(s)) may be signaled in VPS or SPS. FIG. 17shows an example of the syntax elements in VPS and SPS. In this example,vps_sub_picture_dividing_flag is signaled in VPS. The flag may indicatewhether input picture(s) are divided into multiple sub-regions or not.

When the value of vps_sub_picture_dividing_flag is equal to 0, the inputpicture(s) in the coded video sequence(s) corresponding to the currentVPS may not be divided into multiple sub-regions. In this case, theinput picture size may be equal to the coded picture size(pic_width_in_luma_samples, pic_height_in_luma_samples), which issignaled in SPS.

When the value of vps_sub_picture_dividing_flag is equal to 1, the inputpicture(s) may be divided into multiple sub-regions. In this case, thesyntax elements vps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples are signaled in VPS. The values ofvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples may be equal to the width and heightof the input picture(s), respectively.

In the same embodiment, the values of vps_full_pic_width_in_luma_samplesand vps_full_pic_height_in_luma_samples may not be used for decoding,but may be used for composition and display.

In the same embodiment, when the value of vps_sub_picture_dividing_flagis equal to 1, the syntax elements pic_offset_x and pic_offset_y may besignaled in SPS, which corresponds to (a) specific layer(s). In thiscase, the coded picture size (pic_width_in_luma_samples,pic_height_in_luma_samples) signaled in SPS may be equal to the widthand height of the sub-region corresponding to a specific layer. Also,the position (pic_offset_x, pic_offset_y) of the left-top corner of thesub-region may be signaled in SPS.

In the same embodiment, the position information (pic_offset_x,pic_offset_y) of the left-top corner of the sub-region may not be usedfor decoding, but may be used for composition and display.

In the same or another embodiment, the layout information (size andposition) of all or sub-set sub-region(s) of (an) input picture(s), thedependency information between layer(s) may be signaled in a parameterset or an SEI message.

FIG. 18 shows an example of syntax elements to indicate the informationof the layout of sub-regions, the dependency between layers, and therelation between a sub-region and one or more layers. In this example,the syntax element num_sub_region indicates the number of (rectangular)sub-regions in the current coded video sequence. According to anembodiment, the syntax element num_layers may indicate the number oflayers in the current coded video sequence. The value of num_layers maybe equal to or greater than the value of num_sub_region. When anysub-region is coded as a single layer, the value of num_layers may beequal to the value of num_sub_region. When one or more sub-regions arecoded as multiple layers, the value of num_layers may be greater thanthe value of num_sub_region. The syntax elementdirect_dependency_flag[i][j] indicates the dependency from the j-thlayer to the i-th layer. The num_layers_for_region[i] indicates thenumber of layers associated with the i-th sub-region. Thesub_region_layer_id[i][j] indicates the layer_id of the j-th layerassociated with the i-th sub-region. The sub_region_offset_x[i] andsub_region_offset_y[i] indicate the horizontal and vertical location ofthe left-top corner of the i-th sub-region, respectively. Thesub_region_width [i] and sub_region_height[i] indicate the width andheight of the i-th sub-region, respectively.

In one embodiment, one or more syntax elements that specify the outputlayer set to indicate one of more layers to be outputted with or withoutprofile tier level information may be signaled in a high-level syntaxstructure, e.g. VPS, DPS, SPS, PPS, APS or SEI message. Referring toFIG. 19 , the syntax element num_output_layer_sets indicating the numberof output layer set (OLS) in the coded vide sequence referring to theVPS may be signaled in the VPS. For each output layer set,output_layer_flag may be signaled as many as the number of outputlayers.

In the same embodiment, output_layer_flag[i] equal to 1 specifies thatthe i-th layer is output. vps_output_layer_flag[i] equal to 0 specifiesthat the i-th layer is not output.

In the same or another embodiment, one or more syntax elements thatspecify the profile tier level information for each output layer set maybe signaled in a high-level syntax structure, e.g. VPS, DPS, SPS, PPS,APS or SEI message. Still referring to FIG. 19 , the syntax elementnum_profile_tile_level indicating the number of profile tier levelinformation per OLS in the coded vide sequence referring to the VPS maybe signaled in the VPS. For each output layer set, a set of syntaxelements for profile tier level information or an index indicating aspecific profile tier level information among entries in the profiletier level information may be signaled as many as the number of outputlayers.

In the same embodiment, profile_tier_level_idx[i][j] specifies theindex, into the list of profile_tier_level( ) syntax structures in theVPS, of the profile_tier_level( ) syntax structure that applies to thej-th layer of the i-th OLS.

In the same or another embodiment, referring to FIG. 20 , the syntaxelements num_profile_tile_level and/or num_output_layer_sets may besignaled when the number of maximum layers is greater than 1(vps_max_layers_minus1>0).

In the same or another embodiment, referring to FIG. 20 , the syntaxelement vps_output_layers_mode[i] indicating the mode of output layersignaling for the i-th output layer set may be present in VPS.

In the same embodiment, vps_output_layers_mode[i] equal to 0 specifiesthat only the highest layer is output with the i-th output layer set.vps_output_layer_mode[i] equal to 1 specifies that all layers are outputwith the i-th output layer set. vps_output_layer_mode[i] equal to 2specifies that the layers that are output are the layers withvps_output_layer_flag[i][j] equal to 1 with the i-th output layer set.More values may be reserved.

In the same embodiment, the output_layer_flag[i][j] may or may not besignaled depending on the value of vps_output_layers_mode[i] for thei-th output layer set.

In the same or another embodiment, referring to FIG. 20 , the flagvps_ptl_signal_flag[i] may be present for the i-th output layer set.Depending the value of vps_ptl_signal_flag[i], the profile tier levelinformation for the i-th output layer set may or may not be signaled.

In the same or another embodiment, referring to FIG. 21 , the number ofsubpicture, max_subpics_minus1, in the current CVS may be signalled in ahigh-level syntax structure, e.g. VPS, DPS, SPS, PPS, APS or SEImessage.

In the same embodiment, referring to FIG. 21 , the subpictureidentifier, sub_pic_id[i], for the i-th subpicture may be signalled,when the number of subpictures is greater than 1 (max_subpics_minus1>0).

In the same or another embodiment, one or more syntax elementsindicating the subpicture identifier belonging to each layer of eachoutput layer set may be signalled in VPS. Referring to FIG. 22 , thesub_pic_id_layer[i][j][k], which indicates the k-th subpicture presentin the j-th layer of the i-th output layer set. With those information,a decoder may recognize which sub-picture may be decoded and outputtedfor each layer of a specific output layer set.

In an embodiment, picture header (PH) is a syntax structure containingsyntax elements that apply to all slices of a coded picture. A pictureunit (PU) is a set of NAL units that are associated with each otheraccording to a specified classification rule, are consecutive indecoding order, and contain exactly one coded picture. A PU may containa picture header (PH) and one or more VCL NAL units composing a codedpicture.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 or provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 in the CVS, which contains one or more PPSreferring to the SPS, or provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with nuh_layer_id equal to the lowest nuh_layer_id value of thePPS NAL units that refer to the SPS NAL unit in the CVS, which containsone or more PPS referring to the SPS, or provided through externalmeans.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitor provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitin the CVS, which contains one or more PPS referring to the SPS, orprovided through external means or provided through external means.

In the same or another embodiment, pps_seq_parameter_set_id specifiesthe value of sps_seq_parameter_set_id for the referenced SPS. The valueof pps_seq_parameter_set_id may be the same in all PPSs that arereferred to by coded pictures in a CLVS.

In the same or another embodiment, all SPS NAL units with a particularvalue of sps_seq_parameter_set_id in a CVS may have the same content.

In the same or another embodiment, regardless of the nuh_layer_idvalues, SPS NAL units may share the same value space ofsps_seq_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a SPS NALunit may be equal to the lowest nuh_layer_id value of the PPS NAL unitsthat refer to the SPS NAL unit.

In an embodiment, when an SPS with nuh_layer_id equal to m is referredto by one or more PPS with nuh_layer_id equal to n. the layer withnuh_layer_id equal to m may be the same as the layer with nuh_layer_idequal to n or a (direct or indirect) reference layer of the layer withnuh_layer_id equal to m.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In the same or another embodiment, ph_pic_parameter_set_id in PHspecifies the value of pps_pic_parameter_set_id for the referenced PPSin use. The value of pps_seq_parameter_set_id may be the same in allPPSs that are referred to by coded pictures in a CLVS.

In the same or another embodiment, All PPS NAL units with a particularvalue of pps_pic_parameter_set_id within a PU may have the same content.

In the same or another embodiment, regardless of the nuh_layer_idvalues, PPS NAL units may share the same value space ofpps_pic_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a PPS NALunit may be equal to the lowest nuh_layer_id value of the coded sliceNAL units that refer to the NAL unit that refer to the PPS NAL unit.

In an embodiment, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In the same or another embodiment, ph_pic_parameter_set_id in PHspecifies the value of pps_pic_parameter_set_id for the referenced PPSin use. The value of pps_seq_parameter_set_id may be the same in allPPSs that are referred to by coded pictures in a CLVS.

In the same or another embodiment, All PPS NAL units with a particularvalue of pps_pic_parameter_set_id within a PU may have the same content.

In the same or another embodiment, regardless of the nuh_layer_idvalues, PPS NAL units may share the same value space ofpps_pic_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a PPS NALunit may be equal to the lowest nuh_layer_id value of the coded sliceNAL units that refer to the NAL unit that refer to the PPS NAL unit.

In an embodiment, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

Output layer indicates a layer of an output layer set that is output.The output layer set (OLS) indicates a set of layers consisting of aspecified set of layers, where one or more layers in the set of layersare specified to be output layers. The output layer set (OLS) layerindex is an index, of a layer in an OLS, to the list of layers in theOLS.

Sublayer indicates a temporal scalable layer of a temporal scalablebitstream, consisting of VCL NAL units with a particular value of theTemporalId variable and the associated non-VCL NAL units. Sublayerrepresentation indicates a subset of the bitstream consisting of NALunits of a particular sublayer and the lower sublayers.

A VPS RBSP may be available to the decoding process prior to it beingreferenced, included in at least one AU with TemporalId equal to 0 orprovided through external means. All VPS NAL units with a particularvalue of vps_video_parameter_set_id in a CVS may have the same content.

vps_video_parameter_set_id provides an identifier for the VPS forreference by other syntax elements. The value ofvps_video_parameter_set_id may be greater than 0.

vps_max_layers_minus1 plus 1 specifies the maximum allowed number oflayers in each CVS referring to the VPS.

vps_max_sublayers_minus1 plus 1 specifies the maximum number of temporalsublayers that may be present in a layer in each CVS referring to theVPS. The value of vps_max_sublayers_minus1 may be in the range of 0 to6, inclusive.

vps_all_layers_same_num_sublayers_flag equal to 1 specifies that thenumber of temporal sublayers is the same for all the layers in each CVSreferring to the VPS.

vps_all_layers_same_num_sublayers_flag equal to 0 specifies that thelayers in each CVS referring to the VPS may or may not have the samenumber of temporal sublayers. When not present, the value ofvps_all_layers_same_num_sublayers_flag is inferred to be equal to 1.

vps_all_independent_layers_flag equal to 1 specifies that all layers inthe CVS are independently coded without using inter-layer prediction.

vps_all_independent_layers_flag equal to 0 specifies that one or more ofthe layers in the CVS may use inter-layer prediction. When not present,the value of vps_all_independent_layers_flag is inferred to be equal to1.

vps_layer_id[i] specifies the nuh_layer_id value of the i-th layer. Forany two non-negative integer values of m and n, when m is less than n,the value of vps_layer_id[m] may be less than vps_layer_id[n].

vps_independent_layer_flag[i] equal to 1 specifies that the layer withindex i does not use inter-layer prediction.vps_independent_layer_flag[i] equal to 0 specifies that the layer withindex i may use inter-layer prediction and the syntax elements.

vps_direct_ref_layer_flag[i][j] for j in the range of 0 to i−1,inclusive, are present in VPS. When not present, the value ofvps_independent_layer_flag[i] is inferred to be equal toLvps_direct_ref_layer_flag[i][j] equal to 0 specifies that the layerwith index j is not a direct reference layer for the layer with index i.vps_direct_ref_layer_flag [i][j] equal to 1 specifies that the layerwith index j is a direct reference layer for the layer with index i.

When vps_direct_ref_layer_flag[i][j] is not present for i and j in therange of 0 to vps_max_layers_minus1, inclusive, it is inferred to beequal to 0. When vps_independent_layer_flag[i] is equal to 0, there maybe at least one value of j in the range of 0 to i−1, inclusive, suchthat the value of vps_direct_ref_layer_flag[i][j] is equal to 1. Thevariables NumDirectRefLayers[i], DirectRefLayerIdx[i][d],NumRefLayers[i], RefLayerIdx[i][r], and LayerUsedAsRefLayerFlag[j] arederived as follows:

for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0; j <=vps_max_layers_minus1; j++ ) {   dependencyFlag[ i ][ j ] =vps_direct_ref_layer_flag[ i ][ j ]   for( k = 0; k < i; k++ )    if(vps_direct_ref_layer_flag[ i ][ k ] && dependencyFlag[ k ][ j ] )    dependency Flag[ i ][ j ] = 1  }  LayerUsedAsRefLayerFlag[ i ] = 0 }for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0, d = 0, r =0; j <= vps_max_layers_minus1; j++ ) {    (37)   if(vps_direct_ref_layer_flag[ i ][ j ] ) {    DirectRefLayerIdx[ i ][ d++ ]= j    LayerUsedAsRefLayerFlag[ j ] = 1   }   if( dependencyFlag[ i ][ j] )    RefLayerIdx[ i ][ r++ ] = j  }  NumDirectRefLayers[ i ] = d NumRefLayers[ i ] =r }

The variable GeneralLayerIdx[i], specifying the layer index of the layerwith nuh_layer_id equal to vps_layer_id[i], is derived as follows:

for(i=0;i<=vps_max_layers_minus1;i++)  (38)

-   -   GeneralLayerIdx[vps_layer_id[i] ]=i

For any two different values of i and j, both in the range of 0 tovps_max_layers_minus1, inclusive, when dependencyFlag[i][j] equal to 1,it is a requirement of bitstream conformance that the values ofchroma_format_idc and bit_depth_minus8 that apply to the i-th layer maybe equal to the values of chroma_format_idc and bit_depth_minus8,respectively, that apply to the j-th layer.

max_tid_ref_present_flag[i] equal to 1 specifies that the syntax elementmax_tid_il_ref_pics_plus1[i] is present. max_tid_refpresent_flag[i]equal to 0 specifies that the syntax elementmax_tid_il_ref_pics_plus1[i] is not present.

max_tid_il_ref_pics_plus1 [i] equal to 0 specifies that inter-layerprediction is not used by non-IRAP pictures of the i-th layer.max_tid_il_ref_pics_plus1[i] greater than 0 specifies that, for decodingpictures of the i-th layer, no picture with TemporalId greater thanmax_tid_il_ref_pics_plus1[i]−1 is used as ILRP. When not present, thevalue of max_tid_il_ref_pics_plus1[i] is inferred to be equal to 7.

each_layer_is_an_ols_flag equal to 1 specifies that each OLS containsonly one layer and each layer itself in a CVS referring to the VPS is anOLS with the single included layer being the only output layer.each_layer_is_an_ols_flag equal to 0 that an OLS may contain more thanone layer. If vps_max_layers_minus1 is equal to 0, the value ofeach_layer_is_an_ols_flag is inferred to be equal to 1. Otherwise, whenvps_all_independent_layers_flag is equal to 0, the value ofeach_layer_is_an_ols_flag is inferred to be equal to 0.

ols_mode_idc equal to 0 specifies that the total number of OLSsspecified by the VPS is equal to vps_max_layers_minus1+1, the i-th OLSincludes the layers with layer indices from 0 to i, inclusive, and foreach OLS only the highest layer in the OLS is output.

ols_mode_idc equal to 1 specifies that the total number of OLSsspecified by the VPS is equal to vps_max_layers_minus1+1, the i-th OLSincludes the layers with layer indices from 0 to i, inclusive, and foreach OLS all layers in the OLS are output.

ols_mode_idc equal to 2 specifies that the total number of OLSsspecified by the VPS is explicitly signalled and for each OLS the outputlayers are explicitly signalled and other layers are the layers that aredirect or indirect reference layers of the output layers of the OLS.

The value of ols_mode_idc may be in the range of 0 to 2, inclusive. Thevalue 3 of ols_mode_idc is reserved for future use by ITU-T|ISO/IEC.

When vps_all_independent_layers_flag is equal to 1 andeach_layer_is_an_ols_flag is equal to 0, the value of ols_mode_idc isinferred to be equal to 2.

num_output_layer_sets_minus1 plus 1 specifies the total number of OLSsspecified by the VPS when ols_mode_idc is equal to 2.

The variable TotalNumOlss, specifying the total number of OLSs specifiedby the VPS, is derived as follows:

if( vps_max_layers_minus1 = = 0 )  TotalNumOlss = 1 else if(each_layer_is_an_ols_flag | | ols_mode_idc == 0 | | ols_mode_idc = = 1 ) TotalNumOlss = vps_max_layers_minus1 + 1 else if( ols_mode_idc = = 2) TotalNumOlss = num_output_layer_sets_minus1 + 1

vps_all_layers_same_num_sublayers_flag equal to 0 specifies that thelayers in each CVS referring to the VPS may or may not have the samenumber of temporal sublayers. When not present, the value ofvps_all_layers_same_num_sublayers_flag is inferred to be equal to 1.

vps_all_independent_layers_flag equal to 1 specifies that all layers inthe CVS are independently coded without using inter-layer prediction.

ols_output_layer_flag[i][j] equal to 1 specifies that the layer withnuh_layer_id equal to vps_layer_id[j] is an output layer of the i-th OLSwhen ols_mode_idc is equal to 2. ols_output_layer_flag[i][j] equal to 0specifies that the layer with nuh_layer_id equal to vps_layer_id[j] isnot an output layer of the i-th OLS when ols_mode_idc is equal to 2.

The variable NumOutputLayersInOls[i], specifying the number of outputlayers in the i-th OLS, the variable NumSubLayersInLayerInOLS[i][j],specifying the number of sublayers in the j-th layer in the i-th OLS,the variable OutputLayerIdInOls[i][j], specifying the nuh_layer_id valueof the j-th output layer in the i-th OLS, and the variableLayerUsedAsOutputLayerFlag[k], specifying whether the k-th layer is usedas an output layer in at least one OLS, are derived as follows:

NumOutputLayersInOls[ 0 ] = 1 OutputLayerIdInOls[ 0 ][ 0 ] =vps_layer_id[ 0] NumSubLayersInLayerInOLS[ 0 ][ 0 ] =vps_max_sub_layers_minus1 + 1 LayerUsedAsOutputLayerFlag[ 0 ] = 1 for( i= 1, i <= vps_max_layers_minus1; i++ ) {  if( each_layer_is_an_ols_flag| | ols_mode_idc < 2 )   LayerUsedAsOutputLayerFlag[ i ] = 1  else /*(!each_layer_is_an_ols_flag && ols_mode_idc = = 2 ) */  LayerUsedAsOutputLayerFlag[ i ] = 0 } for( i=1; i < TotalNumOlss; i++)  if( each_layer_is_an_ols_flag | | ols_mode_idc = = 0 ) {  NumOutputLayersInOls[ i ] = 1   OutputLayerIdInOls[ i ][ 0 ] =vps_layer_id[ i ]   for( j = 0; j < i && (ols_mode_idc = = 0); j++ )   NumSubLayersInLayerInOLS[ i ][ j ] = max_tid_il_ref_pics_plus1[ i ]  NumSubLayersInLayerInOLS[ i ][ i ] = vps_max_sub_layers_minus1 + 1  }else if( ols_mode_idc = = 1) {   NumOutputLayersInOls[ i ] = i + 1  for( j = 0; j < NumOutputLayersInOls[ i ]; j++ ) {   OutputLayerIdInOls[ i ][ j ] = vps_layer_id[ j ]   NumSubLayersInLayerInOLS[ i ][ j ] = vps_max_sub_layers_minus1 + 1  }  } else if( ols_mode_idc = = 2 ) {   for( j = 0; j <=vps_max_layers_minus1; j++ ) {    layerIncludedInOlsFlag[ i ][ j ] = 0   NumSubLayersInLayerInOLS[ i ][ j ] = 0   }   for( k = 0, j = 0; k <=vps_max_layers_minus1; k++ )     (40)    if( ols_output_layer_flag[ i ][k ]) {     layerIncludedInOlsFlag[ i ][ k ] = 1    LayerUsedAsOutputLayerFlag[ k ] = 1     OutputLayerIdx[ i ][ j ] = k    OutputLayerIdInOls[ i ][ j++ ] = vps_layer_id[ k ]    NumSubLayersInLayerInOLS[ i ][ j ] = vps_max_sub_layers_minus1 + 1   }   NumOutputLayersInOls[ i ] = j   for( j = 0; j <NumOutputLayersInOls[ i ]; j++ ) {    idx = OutputLayerIdx[ i ][ j ]   for( k = 0; k < NumRefLayers[ idx ]; k++ ) {    layerIncludedInOlsFlag[ i ][ RefLayerIdx[ idx ][ k ] ] = 1     if(NumSubLayersInLayerInOLS[ i ][ RefLayerIdx[ idx ][ k] ] <     max_tid_il_ref_pics_plus1[ OutputLayerIdInOls[ i ][ j ] ] )    NumSubLayersInLayerInOLS[ i ][ RefLayerIdx[ idx ][ k ] ] =     max_tid_il_ref_pics_plus1[ OutputLayerIdInOls[ i ][ j ] ]   }  } }

For each value of i in the range of 0 to vps_max_layers_minus1,inclusive, the values of LayerUsedAsRefLayerFlag[i] andLayerUsedAsOutputLayerFlag[i] may not be both equal to 0. In otherwords, there may be no layer that is neither an output layer of at leastone OLS nor a direct reference layer of any other layer.

For each OLS, there may be at least one layer that is an output layer.In other words, for any value of i in the range of 0 to TotalNumOlss−1,inclusive, the value of NumOutputLayersInOls[i] may be greater than orequal to 1.

The variable NumLayersInOls[i], specifying the number of layers in thei-th OLS, and the variable LayerIdInOls[i][j], specifying thenuh_layer_id value of the j-th layer in the i-th OLS, are derived asfollows:

NumLayersInOls[ 0 ] = 1 LayerIdInOls[ 0 ][ 0 ] = vps_layer_id[ 0 ] for(i = 1; i < TotalNumOlss; i++ ) {  if( each_layer_is_an_ols_flag ) {  NumLayersInOls[ i ] =1   LayerIdInOls[ i ][ 0 ] = vps_layer_id[ i ]  }else if( ols_mode_idc = = 0 | | ols_mode_idc = = 1) {   NumLayersInOls[i ] = i + 1   for( j = 0; j < NumLayersInOls[ i ]; j++ )   LayerIdInOls[ i ][ j ] = vps_layer_id[ j ]  } else if( ols_mode_idc == 2 ) {   for( k = 0, j = 0; k <= vps_max_layers_minus1; k++ )    if(layerIncludedInOlsFlag[ i ][ k ] )     LayerIdInOls[ i ][ j++ ] =vps_layer_id[ k ]   NumLayersInOls[ i ] = j  } }

The variable OlsLayerIdx[i][j], specifying the OLS layer index of thelayer with nuh_layer_id equal to LayerIdInOls[i][j], is derived asfollows:

-   -   for (i=0; i<TotalNumOlss; i++)    -   for j=0; j<NumLayersInOls[i]; j++)        -   OlsLayerIdx[i][LayerIdInOls[i][j] ]=j

The lowest layer in each OLS may be an independent layer. In otherwords, for each i in the range of 0 to TotalNumOlss−1, inclusive, thevalue ofvps_independent_layer_flag[GeneralLayerIdx[LayerIdInOls[i][0]]]may beequal to 1.

Each layer may be included in at least one OLS specified by the VPS. Inother words, for each layer with a particular value of nuh_layer_idnuhLayerId equal to one of vps_layer_id[k] for k in the range of 0 tovps_max_layers_minus1, inclusive, there may be at least one pair ofvalues of i and j, where i is in the range of 0 to TotalNumOlss−1,inclusive, and j is in the range of NumLayersInOls[i]−1, inclusive, suchthat the value of LayerIdInOls[i][j] is equal to nuhLayerId.

In an embodiment, The decoding process operates as follows for thecurrent picture CurrPic:

-   -   PictureOutputFlag is set as follows:        -   If one of the following conditions is true,            PictureOutputFlag is set equal to 0:            -   the current picture is a RASL picture and                NoOutputBeforeRecoveryFlag of the associated IRAP                picture is equal to 1.            -   gdr_enabled_flag is equal to 1 and the current picture                is a GDR picture with NoOutputBeforeRecoveryFlag equal                to 1.            -   gdr_enabled_flag is equal to 1, the current picture is                associated with a GDR picture with                NoOutputBeforeRecoveryFlag equal to 1, and                PicOrderCntVal of the current picture is less than                RpPicOrderCntVal of the associated GDR picture.            -   sps_video_parameter_set_id is greater than 0,                ols_mode_idc is equal to 0 and the current AU contains a                picture picA that satisfies all of the following                conditions:                -   PicA has PictureOutputFlag equal to 1.                -   PicA has nuh_layer_id nuhLid greater than that of                    the current picture.                -   PicA belongs to the output layer of the OLS (i.e.,                    OutputLayerIdInOls[TargetOlsIdx][0] is equal to                    nuhLid).            -   sps_video_parameter_set_id is greater than 0,                ols_mode_idc is equal to 2, and                ols_output_layer_flag[TargetOlsIdx][GeneralLayerIdx[nuh_layer_id]                ] is equal to 0.        -   Otherwise, PictureOutputFlag is set equal to            pic_output_flag.

After all slices of the current picture have been decoded, the currentdecoded picture is marked as “used for short-term reference”, and eachILRP entry in RefPicList[0] or RefPicList[1] is marked as “used forshort-term reference”.

In the same or another embodiment, when each layer is an output layerset, PictureOutputFlag is set equal to pic_output_flag, regardless ofthe value of ols_mode_idc.

In the same or another embodiment, PictureOutputFlag is set equal to 0when sps_video_parameter_set_id is greater than 0,each_layer_is_an_ols_flag is equal to 0, ols_mode_idc is equal to 0 andthe current AU contains a picture picA that satisfies all of thefollowing conditions: PicA has PictureOutputFlag equal to 1, PicA hasnuh_layer_id nuhLid greater than that of the current picture and PicAbelongs to the output layer of the OLS (i.e.,OutputLayerIdInOls[TargetOlsIdx][0] is equal to nuhLid).

In the same or another embodiment, PictureOutputFlag is set equal to 0when sps_video_parameter_set_id is greater than 0,each_layer_is_an_ols_flag is equal to 0, ols_mode_idc is equal to 2, andols_output_layer_flag[TargetOlsIdx][GeneralLayerIdx[nuh_layer_id] ] isequal to 0.

FIG. 23 shows an example of the syntax table to indicate the outputlayer set with output layer set mode according to an embodiment.

FIG. 24 shows a block diagram of the decoding process for a bitstream,according to an aspect of the disclosure. In particular, FIG. 24 shows adecoder-side flow chart for indicating the output layer set with outputlayer set mode according to an embodiment.

According to an aspect of the disclosure, a method of decoding maycomprise: receiving a bitstream comprising compressed video/image data(Operation 1001 in FIG. 24 ). The bitstream may have multiple layers.

The method of decoding may further comprise an Operation 1002 of parsingor deriving, from the bitstream, an output layer set mode indicator(e.g., ols_mode_idc) in a video parameter set (VPS).

The method of decoding may further comprise an Operation 1003 ofidentifying output layer set signaling based on the output layer setmode indicator.

The method of decoding may further comprise an Operation 1004 (e.g.,Operations 1004A, 1004B, or 1004C) of identifying one or more pictureoutput layers based on the identified output layer set signaling.

The method of decoding may further comprise an Operation 1005 ofdecoding the identified one or more picture output layers. The decodedone or more picture output layers may be displayed.

The identifying of the output layer set signaling based on the outputlayer set mode indicator may include: in a case that the output layerset mode indicator in the VPS is a first value, identifying a highestlayer in the bitstream as the one or more picture output layers (See,e.g., FIG. 25A); in a case that the output layer set mode indicator inthe VPS is a second value, identifying all layers in the bitstream asthe one or more picture output layers (See, e.g., FIG. 25B); and in acase that the output layer set mode indicator in the VPS is a thirdvalue, identifying the one or more picture output layers based onexplicit signaling in the VPS (See, e.g., FIG. 25C).

FIGS. 25A-25C show the output picture as underlined. As shown in FIGS.25A-25C, there may be five layers in the bitstream and only certainlayers are output to the display. For example, Layer 3 could be output(see, e.g., FIG. 25C).

According to an embodiment, an Ols_mode_idc in VPS may indicate themethod (mechanism) that signals output layer set. For example, if equalto 0, the highest layer in the bitstream may be the only output layer,if equal to 1, all layers in the bitstream may be output layers, and ifequal to 2, one or more output layers may be explicitly signaled in VPS.That is, the picture output may be determined by output layer setsignaling.

For example, the picture output of each layer may be determined byoutput layer set signaling, and the method of output layer signaling maybe determined by ols_mode_idc.

According to an embodiment, each bitstream may be signaling the outputlayer mode and the output layer mode can change from time to time.

According to an embodiment, as shown in FIG. 25A, there may be 5 layers(Layer 4-Layer 0) in the bitstream. As shown in FIG. 25A, at a time=K,where the output layer set mode indicator (ols_mode_idc)==0, a highestlayer may be output. Thus, as shown in FIG. 25A, at Time=K, the outputpicture in Layer 4 is output. At Time=K+1, Layer 3, which is the highestlayer may be output, etc. for K+2 and K+3.

As shown in FIG. 25B, where the output layer set mode indicator(ols_mode_idc) equals 1, all of the layers may be output, such as, ateach of K through K+3.

As shown in FIG. 25C, explicit signaling may be performed. For example,as shown in FIG. 26 , the picture layer 3 (which is shown as output byunderlining) is the output layer during, for example, the time of Kthrough K+3.

The first value may be different from the second value and may bedifferent from the third value, and the second value may be differentfrom the third value.

The first value may be 0, the second value may be 1, and the third valuemay be 2. However, other values may be used and the disclosure is notlimited to usage of 0, 1 and 2 as described above.

The identifying the one or more picture output layers by the explicitsignaling in the VPS may include: (i) parsing or deriving, from the VPS,an output layer flag, and (ii) setting layers that have the output layerflag equal to 1 be the one or more picture output layers.

The identifying of the output layer set signaling based on the outputlay set mode indicator may include: in a case that the output lay setmode indicator in the VPS is a predetermined value, the output layer setsignaling includes identifying the one or more picture output layersbased on explicit signaling in the VPS.

The identifying the one or more picture output layers by the explicitsignaling in the VPS includes: (i) parsing or deriving, from the VPS, anoutput layer flag, and (ii) setting layers that have the output layerflag equal to 1 be the one or more picture output layers, wherein anumber of the multiple layers is greater than 2.

The output layer set signaling may include identifying the one or morepicture output layers based on the explicit signaling in the VPS whenthe output layer set mode indicator equals 2, and a number of layers ofthe multiple layers is greater than 2.

The output layer set signaling may include identifying the highest layerin the bitstream or all layers in the bitstream as the one or morepicture output layers by inferring the one or more picture outputlayers, when the output layer set mode indicator is less than 2, and thenumber of multiple layers is 2, and the output layer set mode indicatoractually is less than 2, and the number of multiple layers actually is2.

According to an embodiment, a number output layer sets minus1 indicatorin the VPS indicates a number of the output layer set.

According to an embodiment, a VPS maximum layer minus1 indicator in theVPS indicates a number of layers in the bitstream.

According to an embodiment, the output layer set flag [i][j] in the VPSindicates whether a j-th layer of an i-th output layer set is an outputlayer or not.

According to an embodiment, if all of the multiple layers areindependent where a VPS all independent layers flag of the VPS equals 1,the output layer set mode indicator is not signaled, and a value of theoutput layer set mode indicator is inferred to be the second value.

According to an embodiment, when each layer is an output layer set, apicture output flag of the VPS is set equal to a picture output flagsignaled in a picture header, regardless of the value of the outputlayer set mode indicator.

Note: a picture in an output layer may or may not have aPictureOutputFlag equal to 1. A picture in a non-output layer has aPictureOutputFlag equal to 0. A picture with PictureOutputFlag equal to1 is outputted for display. A picture with PictureOutputFlag equal to 0is not outputted for display.

According to an embodiment, a picture output flag is set equal to 0 whena sequence parameter set (SPS) VPS identifier is greater than 0, whichindicates that more than one layer is present in the bitstream, an eachlayer is an output layer set flag of the VPS is equal to 0, whichindicates that the multiple layers in the bitstream are not allindependent, the output layer set mode indicator is equal to 0 and acurrent access unit contains a picture that satisfies all of thefollowing conditions including: having a picture output flag that isequal to 1, having a nuh layer identifier that is greater than that of acurrent picture and belongs to the output layer of the output layer set.

According to an embodiment, a picture output flag of the VPS is setequal to 0 when a sequence parameter set (SPS) of the VPS is greaterthan 0, an each layer is an output layer set flag is equal to 0, theoutput layer set mode indicator is equal to 2, and the output layer setoutput layer flag [Target OLS Index][General Layer Index [nuh layeridentifier] ] is equal to 0.

According to an embodiment, the method may further comprise: controllinga display to display the decoded one or more picture output layers.

According to an aspect of the disclosure, a non-transitorycomputer-readable storage medium storing instructions that, whenexecuted, cause a system or device comprising one or more processors to:receive a bitstream comprising compressed video/image data, wherein thebitstream has multiple layers; parse or derive, from the bitstream, anoutput layer set mode indicator in a video parameter set (VPS); identifyoutput layer set signaling based on the output layer set mode indicator;identify one or more picture output layers based on the identifiedoutput layer set signaling; and decode the identified one or morepicture output layers.

According to an embodiment, the instructions are further configured tocause the system or device comprising the one or more processors to:control a display to display the decoded one or more picture outputlayers.

According to an aspect of the disclosure, an apparatus may comprise: atleast one memory configured to store computer program code; and at leastone processor configured to access the at least one memory and operateaccording to the computer program code. According to an embodiment, thecomputer program code may comprise: receiving code configured to causethe at least one processor to receive a bitstream comprising compressedvideo/image data, wherein the bitstream has multiple layers; parsing orderiving code configured to cause the at least one processor to parse orderive, from the bitstream, an output layer set mode indicator in avideo parameter set (VPS); output layer signaling identifying codeconfigured to cause the at least one processor to identify output layerset signaling based on the output layer set mode indicator; pictureoutput layer identifying code configured to cause the at least oneprocessor to identify one or more picture output layers based on theidentified output layer set signaling; and decoding code configured tocause the at least one processor to: decode the identified one or morepicture output layers.

According to an embodiment, the computer program code may furthercomprise: display control code configured to cause the at least oneprocessor to control a display to display the one or more picture outputlayers.

The techniques for decoding, displaying and signaling adaptiveresolution parameters described above, can be implemented as computersoftware using computer-readable instructions and physically stored inone or more computer-readable media. For example, FIG. 7 shows acomputer system 700 suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 7 for computer system 700 are exemplary innature and are not intended to suggest any limitation as to the scope ofuse or functionality of the computer software implementing embodimentsof the present disclosure. Neither should the configuration ofcomponents be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 700.

Computer system 700 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 701, mouse 702, trackpad 703, touch screen 710,data-glove 704, joystick 705, microphone 706, scanner 707, camera 708.

Computer system 700 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 710, data-glove 704, or joystick 705, but there can also betactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 709, headphones (not depicted)),visual output devices (such as screens 710 to include CRT screens, LCDscreens, plasma screens, OLED screens, each with or without touch-screeninput capability, each with or without tactile feedback capability—someof which may be capable to output two dimensional visual output or morethan three dimensional output through means such as stereographicoutput; virtual-reality glasses (not depicted), holographic displays andsmoke tanks (not depicted)), and printers (not depicted).

Computer system 700 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW720 with CD/DVD or the like media 721, thumb-drive 722, removable harddrive or solid state drive 723, legacy magnetic media such as tape andfloppy disc (not depicted), specialized ROM/ASIC/PLD based devices suchas security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 700 can also include interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (749) (such as, for example USB ports of thecomputer system 700; others are commonly integrated into the core of thecomputer system 700 by attachment to a system bus as described below(for example Ethernet interface into a PC computer system or cellularnetwork interface into a smartphone computer system). Using any of thesenetworks, computer system 700 can communicate with other entities. Suchcommunication can be uni-directional, receive only (for example,broadcast TV), uni-directional send-only (for example CANbus to certainCANbus devices), or bi-directional, for example to other computersystems using local or wide area digital networks. Certain protocols andprotocol stacks can be used on each of those networks and networkinterfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 740 of thecomputer system 700.

The core 740 can include one or more Central Processing Units (CPU) 741,Graphics Processing Units (GPU) 742, specialized programmable processingunits in the form of Field Programmable Gate Areas (FPGA) 743, hardwareaccelerators for certain tasks 744, and so forth. These devices, alongwith Read-only memory (ROM) 745, Random-access memory 746, internal massstorage such as internal non-user accessible hard drives, SSDs, and thelike 747, may be connected through a system bus 748. In some computersystems, the system bus 748 can be accessible in the form of one or morephysical plugs to enable extensions by additional CPUs, GPU, and thelike. The peripheral devices can be attached either directly to thecore's system bus 748, or through a peripheral bus 749. Architecturesfor a peripheral bus include PCI, USB, and the like.

CPUs 741, GPUs 742, FPGAs 743, and accelerators 744 can execute certaininstructions that, in combination, can make up the aforementionedcomputer code. That computer code can be stored in ROM 745 or RAM 746.Transitional data can be also be stored in RAM 746, whereas permanentdata can be stored for example, in the internal mass storage 747. Faststorage and retrieve to any of the memory devices can be enabled throughthe use of cache memory, that can be closely associated with one or moreCPU 741, GPU 742, mass storage 747, ROM 745, RAM 746, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 700, and specifically the core 740 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 740 that are of non-transitorynature, such as core-internal mass storage 747 or ROM 745. The softwareimplementing various embodiments of the present disclosure can be storedin such devices and executed by core 740. A computer-readable medium caninclude one or more memory devices or chips, according to particularneeds. The software can cause the core 740 and specifically theprocessors therein (including CPU, GPU, FPGA, and the like) to executeparticular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 746and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 744), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of decoding, the method comprising:receiving a bitstream comprising compressed video/image data, whereinthe bitstream has multiple layers; parsing or deriving, from thebitstream, a syntax element ols_mode_idc in a video parameter set (VPS);identifying output layer set signaling based on the syntax elementols_mode_idc; identifying one or more picture output layers based on theidentified output layer set signaling; and decoding the identified oneor more picture output layers, the decoding comprising: setting, basedon each layer being an output layer set, a syntax elementPictureOutputFlag of the VPS equal to a syntax element pic_output_flagsignaled in a picture header, regardless of the value of the syntaxelement ols_mode_idc, or setting the syntax element PictureOutputFlag ofthe VPS equal to 0 based on a syntax element sps_video_parameter_set_idbeing greater than 0, a syntax element each_layer_is_an_ols_flag beingequal to 0, and the syntax element ols_mode_idc being equal to
 2. 2. Themethod of claim 1, wherein the identifying of the output layer setsignaling based on the syntax element ols_mode_idc includes: in a casethat the syntax element ols_mode_idc in the VPS is a first value,identifying a highest layer in the bitstream as the one or more pictureoutput layers; in a case that the syntax element ols_mode_idc in the VPSis a second value, identifying all layers in the bitstream as the one ormore picture output layers; and in a case that the syntax elementols_mode_idc in the VPS is a third value, identifying the one or morepicture output layers based on explicit signaling in the VPS, whereinthe first value is different from the second value and different fromthe third value, and the second value is different from the third value.3. The method of claim 2, wherein the first value is 0, the second valueis 1, and the third value is
 2. 4. The method of claim 2, wherein theidentifying the one or more picture output layers by the explicitsignaling in the VPS includes: (i) parsing or deriving, from the VPS, asyntax element output_layer_flag, and (ii) setting layers that have thesyntax element output_layer_flag equal to 1 as the one or more pictureoutput layers.
 5. The method of claim 1, wherein the identifying of theoutput layer set signaling based on the syntax element ols_mode_idcincludes: in a case that the syntax element ols_mode_idc in the VPS is apredetermined value, the output layer set signaling includes identifyingthe one or more picture output layers based on explicit signaling in theVPS.
 6. The method of claim 5, wherein the identifying the one or morepicture output layers by the explicit signaling in the VPS includes: (i)parsing or deriving, from the VPS, a syntax element output_layer_flag,and (ii) setting layers that have the syntax elementoutput_layer_flagequal to 1 as the one or more picture output layers,wherein a number of the multiple layers is greater than
 2. 7. The methodof claim 5, wherein the output layer set signaling includes identifyingthe one or more picture output layers based on the explicit signaling inthe VPS when the syntax element ols_mode_idc equals 2, and a number oflayers of the multiple layers is greater than
 2. 8. The method of claim1, wherein the output layer set signaling includes identifying thehighest layer in the bitstream or all layers in the bitstream as the oneor more picture output layers by inferring the one or more pictureoutput layers, when the syntax element ols_mode_idc is less than 2, andthe number of multiple layers is
 2. 9. The method of claim 8, wherein asyntax element num_output_layer_sets_minus1 in the VPS indicates anumber of the output layer set.
 10. The method of claim 9, wherein asyntax element vps_max_layers_minus1 in the VPS indicates a maximumallowed number of layers in each coded video sequence (CVS) referring tothe VPS.
 11. The method of claim 10, wherein a syntax elementols_output_layer_flag[i][j]in the VPS indicates whether a j-th layer ofan i-th output layer set is an output layer or not.
 12. The method ofclaim 2, wherein if all of the multiple layers in the bitstream areindependent layers that do not have parsing and decoding dependency onanother layer, where a syntax element vps_all_independent_layers_flag ofthe VPS equals 1, the syntax element ols_mode_idc is not signaled, and avalue of the syntax element ols_mode_idc is inferred to be the secondvalue.
 13. The method of claim 1, wherein the decoding comprises thesetting, based on each layer being the output layer set, the syntaxelement PictureOutputFlag of the VPS equal to the syntax elementpic_output_flag signaled in the picture header, regardless of the valueof the syntax element ols_mode_idc.
 14. The method of claim 1, whereinthe decoding comprises the setting the syntax element PictureOutputFlagof the VPS equal to 0 based on the syntax elementsps_video_parameter_set_id being greater than 0, the syntax elementeach_layer_is_an_ols_flag being equal to 0, and the syntax elementols_mode_idc being equal to
 2. 15. The method of claim 1, furthercomprising: controlling a display to display the decoded one or morepicture output layers.
 16. A non-transitory computer-readable storagemedium storing instructions that, when executed, cause a system ordevice comprising one or more processors to: receive a bitstreamcomprising compressed video/image data, wherein the bitstream hasmultiple layers; parse or derive, from the bitstream, a syntax elementols_mode_idc in a video parameter set (VPS); identify output layer setsignaling based on the syntax element ols_mode_idc; identify one or morepicture output layers based on the identified output layer setsignaling; and decode the identified one or more picture output layers,the decoding including: setting, based on each layer being an outputlayer set, a syntax element PictureOutputFlag of the VPS equal to asyntax element pic_output_flag signaled in a picture header, regardlessof the value of the syntax element ols_mode_idc, or setting the syntaxelement PictureOutputFlag of the VPS equal to 0 based on a syntaxelement sps_video_parameter_set_id being greater than 0, a syntaxelement each_layer_is_an_ols_flag being equal to 0, and the syntaxelement ols_mode_idc being equal to
 2. 17. The non-transitorycomputer-readable storage medium of claim 16, wherein the instructionsare further configured to cause the system or device comprising the oneor more processors to: control a display to display the decoded one ormore picture output layers.
 18. The non-transitory computer-readablestorage medium of claim 16, wherein the instructions, when executed,cause the system or the device to identify the output layer setsignaling based on the syntax element ols_mode_idc by: in a case thatthe syntax element ols_mode_idc in the VPS is a first value, identifyinga highest layer in the bitstream as the one or more picture outputlayers; in a case that the syntax element ols_mode_idc in the VPS is asecond value, identifying all layers in the bitstream as the one or morepicture output layers; and in a case that the syntax elementols_mode_idc in the VPS is a third value, identifying the one or morepicture output layers based on explicit signaling in the VPS, whereinwherein the first value is different from the second value and differentfrom the third value, and wherein the second value is different from thethird value.
 19. An apparatus comprising: at least one memory configuredto store computer program code; and at least one processor configured toaccess the at least one memory and operate according to the computerprogram code, the computer program code comprising: receiving codeconfigured to cause the at least one processor to receive a bitstreamcomprising compressed video/image data, wherein the bitstream hasmultiple layers; parsing or deriving code configured to cause the atleast one processor to parse or derive, from the bitstream, a syntaxelement ols_mode_idc in a video parameter set (VPS); output layersignaling identifying code configured to cause the at least oneprocessor to identify output layer set signaling based on the outputlayer set mode indicator; picture output layer identifying codeconfigured to cause the at least one processor to identify one or morepicture output layers based on the identified output layer setsignaling; and decoding code configured to cause the at least oneprocessor to: decode the identified one or more picture output layers,wherein the decoding code is configured to cause the at least oneprocessor to: set, based on each layer being an output layer set, asyntax element PictureOutputFlag of the VPS equal to a syntax elementpic_output_flag signaled in a picture header, regardless of the value ofthe syntax element ols_mode_idc, or set the syntax elementPictureOutputFlag of the VPS equal to 0 based on a syntax elementsps_video_parameter_set_id being greater than 0, a syntax elementeach_layer_is_an_ols_flag being equal to 0, and the syntax elementols_mode_idc being equal to
 2. 20. The apparatus of claim 19, whereinthe computer program code further comprises: display control codeconfigured to cause the at least one processor to control a display todisplay the one or more picture output layers.